GB2493917A - Transmitting data via mtc type terminals in a multicast transmission - Google Patents

Abstract

A method of communicating data between a base station and a plurality of terminal devices in a wireless telecommunications system is described. The method comprises transmitting data from the base station to the plurality of terminal devices in a multicast transmission and transmitting response signals from the terminal devices to the base station to indicate whether or not the respective terminal devices have successfully received the multicast transmission. The use of a multicast transmission provides an efficient mechanism for communicating the same data to a plurality of terminal device, for example as might be desired in a machine-type communication (MTC) network. In combination with this, the use of individual response signals, such as ACK / NACK signalling, from the terminal devices allows the base station, or other entity, such as a machine-type communications (MTC) server, to track which terminal devices have indicated successful receipt of the multicast transmission,and to instigate an appropriate re-transmission protocol accordingly.

Description

IFLECOMMVNICJONS APPARATUS AND METHODS

BACKGROUND OF THE INVENTION

Th.e present invention re]ates to methods, systems and apparatus for transmitting data in mobile telecommunication systems, and in pathculai transmitting data n a multicast transmission., Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined. UMTS and Long Term Evolution (LTE) architecture arc able to support more sophisticated sen'ices than simple voice and messaging sen'iccs offcred by previous generations of mobile telecommunication systems.

For example, with the improved radio interface and enhanced data rates provided by LIE systems. a user is able to enjoy high data rate applications such as mobile video streaming and mobile video con.ferencing that would previously only have, been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.

The anticipated widespread deployment of third and fourth generation networks has led to the parallel development of a class of devices and applications which, rather than taking advantage of the high data rates available, instead take advantage of the robust radio interface and increasing ubiquity of the coverage area. Examples include so-called machine type communication (MIC) applications, which are typified by semi-autonomous or autonomous wireless communication devices (i.e.. MIt devices) communicating small amounts of data on a relatively infrequent basis. Exarrtples include so-called smart meters which, for example, are located in a customer's house and periodically transmit information back to a central MIC server data relating to the customers consumption of a utility such as gas, water, electricity and so on. Further information on characteristics of MIC-type devices ca.n be found., for example, in the corresponding standards, such as FIST TS 122 368 VlO,530 (2011-07) / 3GPP IS 22368 version 105.0 Release To) [1] Multicast data transmission is an established technique for effidently communicating content, for example, streaming media, to multiple recipients in an efficient manner-It can. be foreseen that multicast data transmissions may in future be used more and more, for example, to transmit operational data, e.g. software updaLes, to a plurality of MTC connected to a sei-ver through a wireless network..

Furthermore, whilst it can be convenient for a ten. nina] such as an MTC type terminal to take advantage of the wide coverage area provided by a third or fOurth generation mobile telecommunication network there are at present disadvantages. Unlike a conventional third. or fourth generation terminal device such as a smartphone. an MTC-type terminal is preferably relatively simple arid inexpensive. The type of functions performed by the MTC-typc terminal (e.g collecting and reporting back data) do not require particularly complex processin.g to perform. However, third and fOurth generation mobile telecommunication networks typically employ advanced data modulation techniques on the radio interface which can require more complex arid expensive radio transceivers to implement. It is usually justified to include such complex transceivers in a smariphone as a smartphone wil.l typically require a powerful processor to perform typical sma,rtphone type functions.. However, as indicated above, there is now a desire to use relatively inexpensive and less complex devices to communicate using LTE type networks. In parallel with this drive to provide network accessibility to devices having different operational functionality, e.g.. reduced bandwidth operation, is a. desire to optimise the use of the avaijable bandwidth for communicating with such devices, for example using multieast techniques.

SUMMARY OF THE INVENTION

According to a first as aspect of the invention there is provided a method of communicating data in a wi-eless telecommunications system, the method compnsing: transmitting data fi-om a base station to a plurality of terminal devices in a multicast transmission; and transmitting response signals from respective ones of the terminal devices to the base station in response to the multicast transmission to indicate whether the respective terminal devices have succeasthily received the multicast transmission.

In accordance with some embodiments the method further comprises conveying to respective ones of the terminal devices an indication of an uplink transmission resource to be used for their response signal, for example, an indication of a time, code and / or frequency resource In accordance with some embodiments the indication of an uplink transmission resource is conveyed during a set-up procedure performed when the respective terminal devices connect to the wireless telecommunications system. The set-up procedure may comprise a Radio Resource Connection, request..

In accordance with some embodiments the indication of an uplink transmission resource is conveyed in association with the multicast transrnission In accordance with some embodiments the indication of an uplink transmission resource is conveyed by explicit signalling and in some embodiments the indication is conveyed by implicit signalling, for example, within a radio network identifier.

In accordance with some embodiments the indication of an uplink transmission resource comprises at least one of an indication of a transmission resource within an uplink sub-frame, an indication of an uplink sub-frame, and an indication of an u.plink can-icr..

Tn. accordance with sorn.e embodiments the response signals axe transmitted on a Physical Uplink Control Channel., PUCCH In accordance with some embodiments the response signals are transmitted in an upii.nk sub-flame of the wireless telecommunications system occurring at a time derived from the time of a downl.i.nk sub-frame containing the multicast transmission.

In accordance with some embodiments different ones of the terminal devices transmit their response signals in different uplink sub-flames and I or carriers of the wireless telecommunications system.

In accordance with seine embodiments the method further comprises determining from the response signals received at the base station whether any tenninal device has not received the niulticast transmission, and if so, rc4ransmitting the dat.a from the base station.

In accordance with some embodithents the response signals from different ones of the terminal deviccs are transmitted using different uplink transmission resources..

In accordance with sonic embodiments the wireless telecommunications system may implement a virtual carrier such that the system operates in downiink over a. first frequency bandwidth and in uplink over a second frequency bandwidth, and wherein the multicast transmission is made using downlink transmission tesources on frequencies selected forn within a third frequency bandwidth which is smaller than and within the first frequency bandwidth; and wherein the response signals from the terminal devices are transmitted using uplink transmission resources on frequencies selected from within a fourth frequency bandwidth which is smaller than and within the second frequency bandwidth.. Furthennore, the first and second frequency bandwidths may be the same width and I or the third and fourth 1 5 frequency bandwidths may be the sante width.

According to another aspect of th.e invention there is provided a wireless telecommunications system comprising a base station and a plurality of terminal devices.

wherein the base station, is configured to transmit data to a plurality of terminal devices in a multicast ti-ansmission, and wherein the terminal devices are configured to transmit response signals to the base station in response to the mulficast transmission to indicate whether they have successfully received the multicast transmission.

According to another aspect of the invention there is provided a method of operating a base station for communicating data in a wireless telecommunications system, the method comprising: transmitting data to a plurality of terminal devices in. a multicast transmission; and receiving response signals from respective ones of the terminal devices transmitted in response to the multicast transmission to indicate whether the respective terminal devices have successMly received the multicast transmission..

According to another aspect of the invention there is provided a base station for communicating data with a plurality of terminal devices in a wireless telecommunications system, wherein the base station is configured to transmit data to the plurality of terminal devices in a multicast transmission, and wherein the base station is Jiirther configured to receive response signals transmitted hy respective ones of the terminal devices in response to the multicast transmission to indicate whether they have successfully received the multicast U ansmission.

According to another aspect of the invention there is provided a According to another aspect of the invention there is prox'ided a method of operating a terminal device for the communication data in a wireless telecommunications system, the method comprising: receiving data transmitted by a base station to a plurality of temunal devices in a multicast transmission; and transmitting a response signal La the base station in response to the multicast transrnissio]l to indicate whether the terminal device successfully received the multicast transmission.

According to another aspect of the invention there is provided a terminal device for receiving data in a wireless telecommunications system, wherein the terminal device is configured to receive data transmitted by a base station to a plurality of terminal devices in a multicast transmission, and wherein the terminal device is ffirther configured to transmit a response signal to the base station in response to the multicast transmission to indicate whether the terminal device successfully received the multicast transmission.

It will be appreciated that features and aspects of the invention described above in relation to the first and other aspects of the invention are equally applicable and ma.y be combined with embodiments of the invention according to the different aspects of the invention as appropnate, and not just in the specific combinations described above.

BRIEF DESCRIPTION OF' DRAWTINGS

Embodiments of the present invention will now be described by way of example only with reference to the accornpaJing drawings where like parts are provided with corresponding reference numerals and in which: S Figure 1 provides a schematic diagram illustrating an example of a conventional mobile telecommunication network; Figure 2 provides a schematic diagram illustrating a conventional LTF radio frame; Figure 3 provides a schematic diagram illustrating an example of a conventional LTE downhnk radio subframe; Figure 4 provides a schematic diagram illusbating a conventional LTE "camp-on" procedure; Figure 5 provides a schematic diagram illustrating an LTE downlink radio sub-flame in which a virtual cairjer has been inserted in accordance with an embodiment of the invention; Figure 6 provides a schematic diagram illustrating an adapted LIE "camp-on" procedure for camping on to a virtual carrier; Figure 7 provides a schematic diagram illustrating LTE downlink radio sub-frames in accordance with an embodiment of the present invention; Figure 8 provides a schematic diagram illustrating a physical broadcast channel (PBCH); Figure 9 provides a schematic diagram illustrating an LTE downlink radio sub-frame in accordance with an embodiment of the present invention; Figure 10 provides a schematic diagram illustrating an LIE downlink radio sub-frame in which a virtual carrier has been inserted in accordance with an embodiment of the invention; Figures ii A to I 1D provide schematic diagrams illustrating positioning of location si.gual s within a LTE downlink sub-frame according to embodiments of the present invention; Figure 12 provides a schematic diagram illustrating a group of sub-frames in which two virtual carriers change location within a host carrier baud according to an embodiment of the present invention; Figures 13A to 13C provide schematic diagrams illustrating LIE uplinic sub-frames in which an uplink virtual can-icr has been inserted in accordance with an embodiment of the Present invention; Figure 14 provides a schemati.c diagram showing part of an adapted LTE mobile telecommunicatIon network arranged iii accordance with an eximple of the present invention; Figui-e 15 schematically represents an example allocation of transmission resources between a host and virtual carrier fbr both uplink and downilnlc in a L.TE mobile telecommunication network arranged according to an embodiment of the invenl:ion; Figure 16 schematically shows a mobile telecommunication networic architecture configured to operate in accordance with an embodiment of the invention; Figure 1 lÀ schematically represents allocated resources for downlink transmissions and associated uplinic acknowledgement / non-aclcnowledgernent signals for a virtual cairier; Figure 1 7B schematically represents available resources for a Physical Uplink Control Channel (PUCCI-1) for a virtual cather; Figure 1 SA schematically represents allocated resources for downlinlc multicast transmissions and. associated uplirilc acknowledgement I non-acknowledgement signals according to various embodiment of the invention; Figure 1 SB is a ladder! diagram schematically representing a signalling mechanism for causing different terminal devices to send uplinic acknowledgement I non-acknowledgement signalling associated with downlinlc multicast transmissions using different transmission resources; Figures 19 and 20 schematically represent allocated resources for downhnk multicast tTansmnissions and associated uplink acknowledgement / non-acknowledgement signalling according to different embodiment of the invention; and Figures 21 and 22 are ladder diagrams schematically representing mechanisms for causirg different terminal devices to send uplinic acknowledgement I non-acknowledgement signalling associated with downlinJc multicast transmissions using diffejent transmission resources..

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention may in particular be employed within the context of what might be termed "virtual carriers" operating within a bandwiclih of a "host can-iers". The concepts of virtual carriers are described in co-pending 15K. patent applications numbered GB 1101970.0 [2], GB 1101981.7 [3], GB 1 10196&8 [4], GB 11019833 [5], GB 1101853.8 [61, (lB 11019825 [7], GB 1101980.9 [8] and GB 1101972.6 [9], the contents of which are incorporated herein by reference. The reader is referred to these co-pending applications fbr more details, but for ease of reference an overview of the concept of virtual. carders is also provided here.

Conventional Netivoric Figure 1 provides a schematic diagram illustrating some basic functionality of a conventional mobile telecommunications networ-k, Th.e network includes a plurality of base stations 1.01 connected to a core network 102.

Each base station provides a coverage area 1(13 (i.e. a cell) within which data can be communicated to and from terminal devices 104.. Data is transmitted from base stations 101 to terminal devices 104 within their respective coverage areas 103 via a radio downlink, Data is transmitted flom terminal devices 104 to the base stations 101 via a radio uplink.. The core netwoik 102 routes data to and from the terminal devices 104 via the respective base stations 101 and provides functions such as authentication, mobility management, charging and so on.

Mobile telecommunications systems such as those arranged in accordance with the 3GPP defined Long Term Evolution (LTF.) architecture use an orthogonal frequency division multiplex (OFDM) based interface for the radio downli.nk (so-called OFDMA) and the radio uplink. (so-called SC-FDMA). Figure 2 shows a schematic diagram illustrating an OFDM based LTE downlink radio frame 201.. The LTE downlink radio frame is frananiitted from an LIE base station (known as an enhanced Node B) and lasts 10 ms. The downlink radio frame comprises ten sub-frames, each sub-frame lasting I ins, A primary synchronisation signal (PBS) and a secondary synchronisation signal (BBS) are transmitted in the first and sixth sub- frames of the LIE frame. A prmary broadcast channel (PBCH) is transmitted in the first sub-frame of the LIE frame, The PBS, 585 arid PBCFT arc discussed in more detail below..

Figure 3 is a schematic diagram of a grid which illustrates the structure of an example conventional dowulink LIE sub-flame. The sub-frame comprises a predetermined number of symbols which are transmitted over a Ims period.. Each symbol comprises a predetermined number of orthogonal sub-carriers distributed across the bandwiWh of Ihe downlink i-adio carrier The example sub-frame shown in Figure 3 comprises 14 symbols and 1200 sub-carriers spread across a 2OMFIz bandwidth, The smallest allocation of user data for S transmission in L.TE is a resource block comprising twelve sub-carriers transmitted over one slot (0.5 sub-frame). For clarity, in Figure 3. each individual resource element is not shown.

instead each individual box in tie sub-frame grid corresponds to twelve sub-carriers transmitted on. one symbol.

Figure.3 shows in hatching resource allocations for four LTE terminals 340, 341, 342, 343. For example, the resource allocation 342 fbr a first LIE teminal (UE 1) extends over five bloclcs of twelve sub-carriers (i e. 60 sub-carriers), the resource allocation 343 for a second LTE terminal (UF2) extends over six bloelca of twelve subcarricrs and so on.

Control channel data is transmitted in a control region 300 (indicated by dotted-shading in Figure 3) of the sub-frame comprising the first a symbols of the sub-frame where n caji van' between one and three symbols for channel bandwidths of 3MHz or greater and where n can vary between two and four symbols for channel bandwidths of I. 4M}Iz,. For the sake of providing a concrete example, the following description relates to host carriers with a channel bandwidth of 3M1-Iz or greater so the maximum value of 11 will be 3.. The data transmitted in the control region 300 includes data transmitted on the physical downlinlc eonhol channel (PDCCH), the physical control format indicator channel (PCFJCH) and the physical FIARQ indicator channel (PHICH)..

PDCCH conl:ains control data indicating which sub-carriers on which symbols of the sub-frame have been. allocated to specific LTE terminals. flius, the PDCCI-i data transmitted in the contiol region.300 of the sub-frame shown in Figure 3 would indicate that UEI has been allocated the block of resources identified by reference numeral 342, that UE2 has been allocated the block of resources identified by reference numeral 343, and so on.

PCFICH contains control data indicating the size of the control region (i.e. between one arid three symbols)..

PHICH contains HARQ (Flybrid Automatic Request) data indicating whether or not previously transmitted uplink data has been successfully received by the network..

Symbols in a central band 310 of the time-frequency resource grid are used for the transmission of information including the primary synchronisation signal (PSS), the secondary synchronisation signal (SSS) and the physical broadcast channel (PBCH). This central band 310 is typically 72 sub-carriers wide (corresponding to a transmission bandwidth of 1.08 MJ-Iz). The P88 and SSS are synchronisation signals that once detected allow an LTF.

terminal device to achieve frame synchronisation and determine the cell identity of the S enhanced Node B transmitting the downlink signal.. The PBCH carries information about the cell, comprising a master information block (MIB) that includes parameters that I,TE terminals use to properly access the cell.. Data transmitted to individual LIE terminals on the physical dowiilinlc shared channel (PDSCH) can be transmitted in other resource elements of the sub-frame.. Further explanation of these channels is provided below.

1 0 Figure 3 also shows a region of PDSCH containing system infonnation and extending over a bandwidth of R3. A conventional LIE frame will also include reference signals which are discussed further below but not shown in Figure 3 in the interests of clarity.

The number of sub-carriers in an L,TE channel can vaiy depending on the configuration of the transmission network. Typically this variation is from 72 sub carriers contained within a l.,41v11Iz channel bandwidth to 1.200 sub-carriers contained within a 20M1-lz channel bandwidth (as schen atically shown in Figure 3), As is known in the art, data transmitted on the PDCCH, PCFICB and PHJCR is typically distributed on the sub-carriers CEO55 tile entire bandwidth of the sub-frame to provide for frequency diversity. Therefore a conventional LIE terminal must be able to receive the entire channel bandwidth in order to receive and decode the control region.

Figure 4 illustrates an LTE "camp-on" process, that is, the process followed by a terminal so that it can decode downlink transmissions which are sent by a base station via a down.link channel. Using this process, the termina.l can identi' the parts of the transmissions that includ.e system information for the cell and thus decode configuration information for the celL As can be seen in Figure 4, in a conventional LYE camp-on procedure, the terminal first synchronizes with the base station (step 400) using the PSS arid 888 in the centre band and then decodes the PBCH (step 40i). Once th.e terminal has performed steps 400 and 401, it is synchronized with the base station..

For each sub-frame, the terminal then decodes the PCFJCH which is distributed across tue entire bandwidth of carrier 320 (step 402). As discussed above, an LIE downlink carrier can be up to 20 MHz wide (1200 sub-carriers) and. an LTE terminal therefore has to have the capability to receive and decode transmissions on a 20 MHz bandwidth in order to decode the PUFICH At the PCFICH decoding stage, with a 20MHz eanTier band, the terminal operates at a much larger bandwidth (bandwidth of R320) than during steps 400 and 401 (bandwidth o R31n) relating to synchronization and PBCH decoding.

The terminal then ascertains the PHICH locations (step 403) and decodes the PDCCH (step 404), in particular fbr idcnti'ing system infonnation transmissions and for identifying its personal allocation grants. The allocation grants are used by the terminal to locate system information and to locate its data in the PDSCH Both system inform ation and personal allocations are transmitted on PDSCH and scheduled within the carrier band 320.. Steps 40.3 and 404 also require the terminal to operate on the entire bandwidth R320 of the carrier band.

At steps 402 to 404, the terminal decodes information containcd in the control region 300 of a sub-frajne As explained above, in LIE, the three control channels mentioned above (PCFICH, PHICH and PDCCH) can he found across the control region 300 of the carrier where the control region extends over the range R320 and occupies the first one, two or three OFDM symbols of each sub-ftarne as discussed above. In a. sub-frame, typicall.y the control channels do not use all the resource elements within the control region 300, but they are scattered across the entire region, such that a LTE terminal, has to be able to simultaneously receive the entire control region 300 for decoding each, of the three control channels..

The terminal can then decode the PDSCH (step 405) which contains system information or data transmitted for' this terminal.

As explained above, in a.n LTE sub-frame the PDSCH generally occupies groups of resource elements which are neither in the control region nor in the resource elements occupied by P55, SSS or P'BCH. The data in the blocks of resource elements 340, 341, 342, 343 allocated to the different mobile communication tenninai.s (UEs) shown in Figure 3 have a smaller bandwidth than the bandwidth of the entire calTier, although to decode these blocks a terminal first receives the PDCCH spread across the frequency range B320 to determine if the PDCCH indicates that a PDSCH resource is allocated to the lIE and should he decoded. Once a UE has received the entire sub-frame, it can then decode the PDSCH in the relevant frequency range (if any) indicated by the PDCCH. So for example, TIE I discussed above decodes the whole control region 300 and then the data in the resource block 342.

Virtual Downlinlc Carrier Certain classes of devices, such as MTC devices (e.g. semi-autonomous or autonomous wireless communication devices such as smart mcters as discussed above), support communication applications that are characterised by the transmission of smal.l amounts of data at relatively infrequent intervals and can thus be considerably less complex than conventional LYE terminals.. In many scenarios, providing low capability terminals such as those with a conventional high-performance LIE receiver unit capable of receiving and piocessing data florn an LIE downlink frame across the thU carrier bandwidth can be overly complex for a device which only needs to communicate small amounts of data. This may therefore limit the practicality of a widespread deployment of low capability MIC type devices in an LTE network. It is preferable instead to provide low capability terminals such as MTC devices with a simpler receiver unit which. is more proportionate with the amount of data likely to he transmitted to the terminal, As set out below, in accordance with examples of the present invenficn a "virtual carrier" is provided within the transmission resources of a conventional 01DM type downlink carrier (i.e. a "host carrier"), Unlike data transmitted on a conventional OFDM type downlink carrier, data transmitted on the virtual carrier can be received and decoded without needing to process the Ml bandwidth of the downlink host OFDM carrier. Accordingly, data transmitted on the virtual carrier can be received, and decoded using a reduced complexity receiver unit.

Figure 5 provides a schematic diagram illustrating an LTE downiinlc sub-frame which includes a virtual carrier inserted in a host carrier in. accordance with an example of the present invention..

In keeping with a conventional LTE downlink sub-flame, the first n symbols (n is three in Figure 5) form the control region 300 which is reserved for the transmission of downlink control data such as data tTansnutted on the PDCCH.. However, as can be seen fl-cm Figure 5. outside of the control region..) 00 the LTE downlink sub-frame includes a group of resource elements positioned in this example below the central band 31 0 which form a virtual carrier 501-As explained further below, the virtual carrier 501 is adapted so that data transmitted on the virtual can-icr 501 can be treated a.s logically distinct from data transmitted in the remaining parts of the host carrier and can be decoded without decoding all the control data from the control region 300. Although Figure 5 shows the virtual carrier-occupying frequency resources below the centre hand, in general the virtual carrier can occupy other frequency resources, for example, above the centre band or including the centre band. If the 1' J3 virtual carrier is configured to overlaiD any resources used by the PSS, SSS or PBCH of the host carder, or any other signal transmitted by the host carder that a temrinal device operating on the host carrier would require for correct operation and expect to find in a lcnown pit-determined location, the signals on the virtual carrier can be an:anged such that these aspects of the host carrier signal are maintained.

As can he seen from Figure 5, data transmitted on the virtual carrier 501 is transmitted across a limited bandwidth.. Tins might be any suitable bandwidth smaller than that of the host carrier. in the example shown in Figure 5 the virtual carrier is transmitted across a bandwidth comprising 12 blocks of. 12 sub-carriers (i.e. 144 sub-carriers), which is equivalent to a 2.16MHz transmission bandwidth. Accordingly, a terminal using the virtual carder need only be equipped with a receiver capable of receiving and processing data transmitted over a bandwidth of 2.1 6MHz, This enables low capability terminals (for example MTC type terminals) to he provided with simplified receiver units yet still be able to operate within an UFDM type communication nthvork which, as explained above, conventionally requires terminals to be equipped with receivers capable of receiving and processing an. OFDM signal across the entire bandwidth of the signal.

As explained above, iii OFDM-based mobile communication systems such as LIE, downlink data is dynamically assigned to be transmitted on different sub-carriers on a. sub- frame by sub-frame basis. Accordingly, in every sub-frame the network signals which sub-carriers on which symbols contain data relevant to which terminals (i.e. downlink gant signalling).

As can be seen from Figure 3, in a conventional downlink LTE sub-frame this information is transmitted on the PDCCH during the first symbol or symbols of the sub-frame. However, as previously explained, the information transmitted in the PDCCH is spread across the entire bandwidth of the sub-frame and therefore cannot be received by a mobile communication terminal with a simplified receiver unit capable only of receiving the reduced bandwidth viñual carrier Accordingly, as can be seen in Figure 5, the final symbols of the virtual carrier can be reserved as a control region 502 for the virtual can-icr for the transmission of coitol data indicating which resomce elements of the virtual carrier 501 have been allocated to user equipment (UEs) using the virtual carrier. In some examples the number of symbols comprising the virtual carrier control region 502 migh.t be fixed, fbr example three symbols.

In other examples the virtual carrier control region 502 can vary in size, for example between one and three symbols, as with the control legion 300.

The virtual carrier control region ca.n be located at any suitable position. for example in the tb-st few srnibols of the virtual carrier.. In the example of Figure 5 this could mean positioning the virtual carrier control region on the fourth, fifth mid sixth symbols. However, fixing the position of the virtual carrier control region in the final symbols of the sub-frame can be usethl because the position of the virtual carrier conl.i-ol region will not vai-y in dependence on the number of symbols of the host can-icr control region.300. This can help simplify the processing undertaken by mobile communication terminals receiving data on the 1 0 virtual carrier because there is no need for terminals to determine a position of the virtual carrier control region every sub-frame if it is known that it will always be positioned in the final n symbols of the sub-frame In a further embodiment, the virtual carrier control symbols may refbrence virtual carrier PDSCH transmissions in a separate sub-frame.

In some examples the virtual carrier may be located within the centre band 310 of the downlink sub-frame.. This can help reduce the impact on host carrier PDSCI-{ resources caused by the introduction of the virtual carrier within the host carrier bandwidth since the resources occupied by the PSSISSS and PECH would be contained within the virtual carrier region and not the remaining host carrier PDSCH region. Therefore, depending on for example the expected virtual carrier throughput, the location of a virtual carrier can be appropriately chosen to either exist inside or outside the centre band according to whether the host or virtual carrier is chosen to bear the overhead of the PSS, SSS and PECH.

\TjjpjJ Carrier "Camp-On" Process As explained above, before a conventional LTE terminal can begin transmitting and receiving data in a cell, it first camps on to the cell An adapted camp-on process can he provided for terminals using th.e virtual carrier..

Figure 6 shows a flow diagram schematically illustrating a camp-on process according to an example of the present invention. There are two branches shown in Figure 6. Different steps of the process associated with a UP intending to use the virtual carrier are shown under the general heading "virtual carrier" The steps shown under the general heading "legacy LIE" are associated with a UP intending to use the host carrier, and these steps correspond to 1.5 the steps of Figure 4 In this example, the first two steps 400, 40] of the camp-on procedure are common to both the virtual carrier and host (legacy LIE) can-icr..

The virtual carrier camp-on process is explained with. reference to the example sub-flame shown in. Figure 5 in which a virtual carrier with a bandwidth of 144 sub-carriers is inserted within the operating bandwidth of a host can-icr with a bandwidth coiresponding to 1200 sub-carriers. As discussed above, a terminal having a receiver unit with an operational bandwidth of less than that of the host eanier cannot fully decode data in the contiol region of sub-flames of the host carrier. However, a receiver unit of a terminal having an operational bandwidth of only twelve blocks of twelve sub-carriers (i.e 2 16 MHz) can receive control and user data transmitted on this example virtual carrier 502.

As noted above, in the example of Figure 6, the first steps 400 and 401 for a virtual carrier tenninal are the same as the conventional camp-on process shown in Figure 4, although a virtual carrier terminal may extract additional information from the MIB as described below. Both types of terminals (i.e virtual carrier terminals and host / legacy carrier IS terminals) can use the PSS/SSS and ?BCH to synchronize with the base station using the information carried on the 72 sub-carrier centre band within the host carrier. However, where the conventional LTE terminals then continue with the process by performing the PCFICH decoding step 402, which requires a receiver unit capable of receiving and decoding the host earner control region 300, a terminal camping on to the cell to receive data on the virtual carrier (which may he referred to as a "virtual carrier terminal") performs steps 606 and 607 instead.

In a further embodiment of the present invention a separate synchronisation and PBCH functionality can be provided for the virtual carrier device as opposed to re-using the same conventional initial camp-on processes of steps 400 and 401 of the host carrier device.

At step 606, the virtual canier terminal locates a virtual carrier, if any is provided within the host carriei, using a virtual carrier-specific step.. Various examples of how this step may be performed are discussed further below. Once the virtual carrier terminal has located a virtual carrier, it can access information within the virtual carrier. For example, if the virtual carrier' minors the conventional LIE resource allocation method, the virtual carrier terminal may proceed to decode control portions within the virtual carrier, which can, for example, indicate which resource elements within the virtual carrier have been allocated for a specific virtual carrier terminal or for system information. For example, Figure 7 shows the bloclcs of resource elements 350 to 352 within virtual carrier 330 that have been allocated for the sub-frame SF2.. However, there is no requireient *for the virtual carrier tenninal to follow or mirror the conventional LIE process (e.g.. steps 402-'104) and these steps may for example he implemented very differently for a virtual carrier camp-on process.

S Regardless of the virtual carder terminal following a LTE-like step or a different type of step when performing step 607, the virtual carrier terminal can then decode the allocated resource elements at step 608 and thereby receive data transmitted by the base station broadcasting the virtual carrier. The data decoded in step 608 may include, for example, the remainder of the system information containing details of the networic configuration..

1 0 Even though the virtual carrier tenrinal does not have the bandwidth capabilities to decode and receive downlink data if it was transmitted in the host carrier using conventional LTE, it can still access a virtual carrier within the host carrier having a limited bandwidth whilst re-using the initial LIE steps. Step 608 may also be implemented in a LIE-like manner or in a different manner. For example, multiple virtual carrier terminals may share a virtual carrier and have grants allocated to manage the virtual carrier sharing as shown in SF2 in Figure 7, or, in another example, a virtual carrier terminal may have the entire virtual carrier allocated for its own downlinic transmissions, or the virtual carder maybe entirely allocated to a virtual carrier terminal for a certain number of sub-frame only, etc. There is thus a large degree of flexibility provided for the virtual carrier camp-on process. There is, for example, the ability to adjust a balance between re-using or mirroring conventional LIE steps or processes, thereby reducing the terminal complexity and the need to implement new elements, and adding new virtual carrier specific aspects or implementations, thereby potentially optimizing the use of narrow-band virtual carriers, as LTE has been designed with the larger-band host carriers in mind.

Dowriiink Virtual Carrier Detection As discussed above, the virtual carrier terminal should locate (within the time-frequency resoui-ce grid of the host carrier) the virtual carrier before it can receive and decode transmissions on the virtual carrier. Several alternatives are available for the virtual carrier presence and location determination, which can he implemented. separately or in combinatiow Some of these options are discussed below..

To facilitate the virtual carrici: detection, the virl:ual carrier location information may be provided to the virtual carrier terminal such that it Carl locate the virtual carrier, it any exists, more easily. For example, such location information may comprise an indication that on.e or more virtual cair cr5 are pro\'ided within the host carrier, or' that the host carder does not cuiTently provide any virtual carder II may also comprise an indication of the virtual carrier's bandwidth, for example in MHz or blocks of resource elements Alternatively, or' in combination, the virtual carrier location information may comprise the virtual carrier's centre frequency and. bandwidth, thereby giving the virtual carder terminal the location an.d bandwidth of any active virtual carrier, In the event the virtual carrier' is to he found at a different frequency position in each sub-frame, accoiding, for example, to a pseudo-random hopping algorithm. the location infOrmation can, for example, indicate a pseudo random parameter.. Such parameters may include a starting frame and parameters used for the pseudo-random algorithm.. Using these pseudo-random parameters, the virtual carrier terminal can then know where the virtual carrier can be found for any sub-frame.

On implementation feature associated with little change to the virtual carrier terminal (as compared with a conventional LTE terminal) would be to include location infbnnation for the virtual carrier within the PBCH, Which already carries the Master Inform-ration Block, or Mifi in the host carrier centre band. As shown in Figure 8, the MS consists of 24 bits (3 hits to indicate DL bandwidth, 8 bits to indicate the System Frame Number or SFN, and 3 bits regarding tEe PHICH configuration).. The MIB thercfote comprises 10 spare bits that can be used to carry location information in respect of one or more vittal carriers. For example, Figure 9 shows an example where the PBCI-i includes the MS and location infonnation ("LI") for pointing any virtual carrier terminal to a virtual carrier.

Alternatively, virtual carrier location information, could be provided in the centre band, outside of the PBCT-I.. It can fbr example be always provided after and ad. jacent to the PBCH.

By providing the location information in th.e centre band but outside of the P801-I, the conventional P808 is not modified for the purpose of using virtual carriers, but a virtual carrier terminal can easily find the location information in order to detect the virtual carrier, if any..

The virtual carrier location information, if provided, can be provided elsewhere in the host carrier, hut it may be advantageous to provide it in the centre band, for example because a virtual carrier terminal may configure its receiver to operate on the centre band and the virtual carrier terminal then does not need to adjust its receiver settings for finding the location information Depending on the amount of virlual carrier location information provided, the virtual carrier terminal can either adjust its receiver to receive the virtual carrier transmissions, or it may require irthe.r location information before it can do so.

If fOr example. the virtual carrier terminal was provided with location information indicating a virtual carrier presence andlor a virtual carrier bandwidth hut not indicating any details as to the exact virtual carrier frequency i-ange, or if [he virtual carrier terminal was not provided with any location information, the virtual carrier terminal cou'd then scan the host carrier for a virtual carrier (e g. performing a so-called blind search process). Scanning the host carrier for a virtual carrier can be based on different approaches, some of which will be presented below..

According to a first approach, a virtual carrier might only he inserted in certain pre-determined locations, as illustrated for example in Figure 10 for a four-locatior. example. The virtual carrier terminal then scans the four locations Li-IA for any virtual carrier-If and when the virtual carrier terminal detects a. virtual carrier, it can then "camp-on" the virtual carrier to receive down.link data as described above. In this approach, the virtual carrier terminal may be provided with the possible virtual carrier locations in advance, for example they may be stored as a network-specific sett ing in an internal memory.. Detection of a virtual carrier could be accomplished by seeking to decode a particular physical channel on the virtual carrier. The successthl decoding of such a channel, indicated for example by a suceessftil cyclic redundancy check (CRC) on decoded data, would indicate the successful locaffon of the virtual carrier According to a second approach, the virtual carrier may include location signals such that a virtual carrier terminal scanning the host carrier can detect such signals to identify the presence of a virtual carrier. Examples of possible location signals are illustrated in Figures hA to 111). In the examples of Figures hA to 11C, the virtual carrier regularly sends an arbthary location signal such that a. tenninal scanning a frequency range where the location signal is would detect this signal. An "arbitrary" signal is intended here to include any signal that does not carry any information as such, or is not meant to be interpreted, but merely includes a specific signal or pattern that a virtual carrier terminal can detect. Thi.s can for example be a series of positive bits across the entire location signal, an alternation of 0 and 1 across the oeation signal, or any other suitable arbitrary signa}. It is noteworthy that the location signal may he nmde of adjacent blocks of resource elements or may be fonned of non adjacent blocks, For example, it may he located at every other block of resource elcinents at the "top" (i.e. uppei frequency limit) of the virtual carrier.

In the example of Figure 1 I A, the location signal 353 extends across the range R33n of the virtual carrier 330 and is always found at the same position in the virtual carrier within a sub-frame. If the virtual carrier terminal knows where to loolc for a location signal in a virtual carder sub-frame, it can then simpli' its scanning process by only scanning this position within a sub-frame for a location signal. Figure II B shows a similar example where every sub-frame includes a location signal 354 comprising two parts: one at the top corner and one at the bottom corner of the virtual carrier sub-frame, at the end of this sub-frame. Such a location signal may be useful if, fbr example, the virtual carrier terminal does not lcnow the bandwidth of the virtual carrier in advance as it can fcilitate a clear detection of the top and bottom frequency edges of the virtual carrier band.

in the example of Figure I1C, a location signal 355 is provided in a first suh-frarn.e SF1, hut not in a second sub-frame SF2-The location signal can for example be provided every two sub-frames. The fiequency of the location signals can be chosen to adjust a balance between rcducing scanning time and reducing overhead. In other words, the mote often the location signal is provided, the less long it takes a terminal to detect a virtual carrier but the more overhea.d there is.

In the example of Figure lID, a location signal is provided where this location signal is not an arbitrary signal as in Figures hA to liC, but is a signal that includes information for virtual can-icr terminals. The virtual carrier terminals can detect this signal when they sczui for a virtual carrier and the signal may include information in respect of for-example. the virtual carrier bandwidth or any other virtual carrier-related infonnation (location or non-location information). When detecting this signal., the virtual can-icr terminal can thereby detect the presence and location of the virtual carrier. As shown in Figure lID, the location signal can.

like an arbitrary location signal, be found at different locations within the sub-frame, and the location may vary on a per-sub-frame basis.

Qypie Variation of Control Region Size of i-lqst Caj As explained above, i.n LIE the number of symbols that malce up the control region of a downiinlc sub-frame var-ics dynamically depending on the quantity of control data that needs to be transmitted. Typically, this variation is between one and three symboi.. As will be understood with reference to Figure 5, variation iii the width of the host cather control region S will cause a corresponding variance in the number of symbols available for the virtual carrier.

For examplc, as can be seen in Figure 5, when the control region is three symbols in length and there arc 14 symbols in the sub-frame, the virtual carrier is eleven symbols long.

However, if in. the next sub-frame the control region of the host carrier were reduced to one symbol, there would be thirteen symbols available for the virtual carrier in that sub-fl-sine..

Wben a virtual carrier is inserted into a LIE host carrier, mobile communication terminals receiving data on the virtual carrier need to be able to determine the number of symbols in the control region of each host carrier sub-frame to determine the number of symbols in the virtual carrier in that sub-frame if they are to be able to use all available symbols that are not used by the host esther control region.

Conventionally, the number of symbols forming the control region. is signalled in the Erst symbol of every sub-frame in the POFICH. However, the PCFICH is typically distributed across the entire bandwidth of the downlink LIE sub-frame and is therefore transmitted on sub-carriers which virtual carrier terminals capable only of receiving the virtual carrier cannot receive.. Accordingly, in one embodiment, any symbols acros.c which the control region could possibly extend axe pr-edefined as null symbols on the virtual carrier, i.e. the length of the virtual sub-carrier is set at (m -n) symbols, where in is the total number of symbols in a sub-frame and ii is the maximum number of symbols of the. control region. Thus, resource elements are never allocated for downlink data transmission on the virtual carrier during the first n symbols of any given sub-frame..

Although this embodiment is simple to implement it will be spectrally inefficient because duiing sub-frames when the control region of the host carrier has fewer than the maximum number of symbols, there will be unused symbols in the virtual can-icr.

In another embodiment, the number of symbols in the control region of the host carrier is explicitly signalled in the virtual can-icr itself. Once the number of symbols in the control region of the host carrier is known, the number of symbols in the virtual carrier can be calculated by subtracting the total number of symbols in the sub-.frame from this number..

In one example an explicit indication of the host carrier control region size is given by certain infdrmation bits in. the virtual earner control region In other words an explicit signalling message is inserted at a predefined position in the virtual carrier control region 502.

This predefined position is known by each terminal adapted to receive data on the virtual C SIT] er In another example. the virtual carrier includes a predefined signal, the location of which indicates the number of symbols in the control region of the host carriers. For example, a predefined signal could be transmitted on one of three predetermined bloclcs of resource elements. When a terminal receives the sub-frame it scans for the predefined signal. If the predefined signal is found in the first bloclc of resource elements this indicates that the control region of the host carrier comprises one symbol.; if the predefined signal is found in the second block of resource elements this indicates that the control region of the host cather comprises two snbols and if the prcdefined signal is found in the third block of resource elements this indicates that the control region of the host carrier comprises three symbols.

hi another example, the virtual carrier terminal is arranged to first attempt to decode the vh-tual carrier assuming that the control region size of the host earner is one symbol. If this is not successflut, the virtual carrier terminal attempts to decode the virtual carrier assuming that the control region size of the host carrier is two an.d so on, until the virtual carrier terminal successfully decodes the virtual carrier.

Downlink \Tirtual Carrier Reference Signals As is known in the art, in OFDM-based transmission systems, such as LTE, a number of sub-carriers in symbols throughout the sub-flames are typically reserved for the transmission of reference signals. The reference signals are transmitted on sub-carriers distributed throughout a sub-frame across the channel bandwidth and aeros.s the OFDM symbols. The reference signals are arranged in a repeatin.g pattern and can he used by a receiver to estimate the channel function applied to the data transmitted on each sub-carrier using extrapolation. and i.nteolation techniques. These reference signals are also typically used for additional purposes such as determining metrics for received signal power indications, automatic frequency control metrics and automatic gain control metrics. In LTE the positions of the reference signal bearing sub-carriers within each sub-frame are pre-defined and are therefore known a.t the receiver of each terminal.

th LIP downlink sub-frames, reference signals from each transmit antenna port are typically inserted oil every sixth sub-carrier.. Accordingly, if a virtual carrier is inserted in an LIE downlinjc sub-frame, even if the virtual carrier has a minimum bandwidth of one resource block (i.e. twelve sub-carriers) the virtual carder will ineltide at least some reference sigmil bearing sub-carriers.

There are sufficient reference signal bearing sub-carriers provided in each sub-frame such that a receiver need not accurately receive evcry single reference signal to decode the data transmitted on the sub-frame. However, as will be understood the more reference signals that are received, the better a receiver will generally be able to estimate the channel response, and hence fewer errors will typically be introduced into the data decoded from the sub-frame.

Accordingly, in order to preserve compatibility with LIE communication terminals receiving data on the host earlier, in accordance with some examples of the present invention, the sub-carrier positions that would contain reference signals in a conventional LIE sub-frame are retained in the virtual carrier.

1 As will be understood, in accordance with examples of the present invention, terminals arranged to receive only the virtual carrier receive a reduced number of sub-card ers compared to conventional LIE terminals which receive each sub-frame across the entire bandwidth of the sub-frame. As a result, the reduced capability terminals receive fewer reference signals over a narrower range of frequencies which may result in a less accurate channel estimation being generated.

In some examples a simplified virtual carrier terminal may have a lower mobility which requires fewer reference symbols to support channel estimation, However, in some examples of the present invention the downiink virtual carder includes additional reference signal bearing sub-carriers to enhance the accuracy of the channel estimation that the reduced capability terminals can generate..

In some examples the positions of the additional reference bearing sub-carriers are such that they are systematically interspersed with respect to the positions of the conventional refCrcnce signal bearing sub-carriers thereby increasing the sampling frequency of th.e channel estimation when combined with the reference signals from the existing reference signal bearing sub-carriers. Ihi.s allows an improved channel estimation of the channel to be generated by the reduced capability tenni.nals across the bandwidth of the virtual carrier.. In other examples, the positions of the additional reference bearing sub-carriers are such that £3 they are systematically placed at the edge of the baiiclwidth of the virtual carrier thereby increasing the interpolation accuracy of the virtual can-icr channel estimates, Alternative Virtual Carrier Arrangements So far examples of the invention have been described generally in terms of a host carrier in which a single virtual earlier has been inserted as shown for example in Figure 5.

However, in some examples a host carrier may include more than one virtual carrier as shown for example in Figure 12. Figure 12 shows an example in which two virtual carriers VCI (330) and VC2 (331) are provided within a host carijer 320 In this example, the two virtual carriers change location within the host carrier band according to a pseudo-random algorithm However, in other examples, one or both of the two virtual carriers may always be found in the same fiequency range within the host carrier frequency range and!or may change position according to a different mechanism. In L.TF., the number of virtual carriers within a host carrier is only limited by the size of the host carrier.. However, too many virtual carriers within the host carrier may unduly limit the bandwidth available for transmitting data to conventional LIE terminals and an operator may thereibre decide on a number of virtual carrier within a host carrier according to, for example. a ratio of conventional LIE users / virtual carder users.

In some examples the number of active virtual carriers can be dynamically adjusted such that it fits the current needs of conventional LIE terminals and virtual carrier terminals.

For exEunple, if no virtual carrier terminal is connected or if their access is to be intentionally limited, the network can arrange to begin scheduling the transmission of data to [TB terminals within the sub-carriers previously reserved for the virtual cairier This process can be reversed if' the number of active virtual carrier terminals begins to increase. In some examples the number of virtual carriers provided maybe increased in response to an increase in the presence of virtual carder terminals. For example if the number of virtual terminals present in a network or area of a network exceeds a threshold value, an additional virtual carrier is inserted in the host carrier. The network elements and/or network operator can thus activate or deactivate the virtual carriers whenever appropriate.

The virtual carrier shown for example in Figure 5 is 144 sub-carriers in bandwidth.

1-lowever, in other examples a virtual carrier may be of any size between twelve sub-earners to 1188 sub-carriers (for a carder with a 1200 sul>carrier fransmnission handwidtii) Because in LTE. the centre hand bag a bandwidth of 72 sub-carriers, a virtual carrier terminal in an LTF. environment preferentially has a receiver bandwidth of at least 72 sub-carriers (1.08 MHz) such that it can decode the centre band 310, therefore a 72 sub-carrier virtual earner may provide a convenient implementation option.. With a virtual carder comprising 72 sub-carriers, the virtual canicr terminal does not have to adjust the receiver's bandwidth fhr camping on the virtual carrier which may therefore reduce complexity of performing the camp-on process, but there is no requirement to have the same bandwidth for the virtual can-icr as for the centre hand and, as explained abovc, a virtual carrier based on LTF. can be of any size between 12 to 1188 sub-carriers. For example, in some systems. a. virtual carrier to having a bandwidth of less than 72 subcarriers may be considered as a waste of the virtual carrier terminal's receiver resources, bu orn another point of view, it may be considered as reducing the impact of the virtual carrier on the host carrier by increasing the bandwidth available to conventional LTE. terminals. The bandwidth of a virtual carrier can therefbre be adjusted to achieve the desired balance between complexity, resource utilization, host carder 1 5 performance and. requirements for virtual carrier terminals.

Uplink Transmission Frame So far, the virtual carrier has been discussed primarily with reference to the dowolink, however in some examples a virtual carrier can also be inserted in the up]ink.

In frequency division duplex (FDD) networks both the uplink and dowulink are active in all sub-frames, whereas in time division duplcx (TDD) networks sub-frames can either he assigned to the uplink, to the downlink, or thither sub-divided into uplink and down].irilc portions In order to initiate a connection to a network, conventional LTE terminals make a random access request on the physical random access channel (PRACH), The PRACFI is located in predetermined blocks of resource elements in the uplink frame, the positions of which are signaled. to the LTE terminals i.n the system information signaled on the d.ownlink.

Additionally, when there is pending uplink data to be transmitted. from an LTE terminal and the terminal does not already have any uplink resources allocated to it, it can transmit a random access request PR.ACH to the base station. A decision is then made at the base station as to which if any uplinic resource is to be allocated to the terminal device that has made the request. Uplink resource allocations are then signaled to the LTE terminal on the physical dowalink control channel (PDCC1i) transmitted in the control region of the dnwnlinic subframe Tn LIE, transmissions from each terminal device a-c constrained to occupy a set of contiguous resource blocics in a frame.. For the physical uplink shared channel (PUSCI-I) the uplink resource allocation grant received from the basc station will indicate which set of resource blocics to use for that ansmission. where these resource bloclcs could be located anywhere within the channel bandwidth The first resources used by the Lit physical uplink control channel (PUCCI-!) are located at both the upper and lower edge of the channel, where each PUOCH tTansmrssion 1.0 occupies one resource block. In the first half of a sub-frame this resource bloclc is located at one channel edge, and in the second half of a sub-frame this resource block is located at the opposite channel edge. As more PUOCH resources are required, additional resource blocks ase assigucd in a sequential manner, moving inward from the channel edges. Since PUCCH signals are code division multiplexed, an LYE uplink can accommodate multiple PUCCH transmissions in the same resource block.

VirjlijçCarrier In accordance with embodiments of the present invention, the virtual carrier terminals described above can also be provided with a reduced capability transmitter for transmitting uplinic data, The virtual carrier terminals are arranged to transmit data across a reduced bandwidth. The provision of a reduced capability transmitter unit provides colTespondrng advantages to those achieved by providing a reduced capability receiver unit with, for example, classes of devices that are manufactured with a reduced capability for use with, for example. MIC type applications.

In correspondence with the downli.nlc virtual carrier, the virtual can-icr terminals transmit uplink data across a reduced range of sub-carriers within a host carrier that has a eater bandwidth than that of the reduced bandwidth virtual carrier. Ibis is shown in Figure I 3A. As can be seen fiom Figure 1 3A, a group of sub-carriers in an uplink sub-flame form a virtual carrier 1301 within a. host carrier 1302. Accordingly, the reduced bandwidth across which the virtual carrier terminals transmit uplink data can be considered a virtual uplink carrier, In order to implement the virtual uplink carrier, the base station scheduler serving a virtual catTier ensures that all uplinlc resouice elements granted to virtual cai-rier terminals are sub-carriers that fall within, the reduced bandwidth range of the reduced capability transmitter units of the virtual carrier terminals. Con-esporidingly, the base station scheduler serving the host carrier typically ensures that all uplink resource elements granted to host can-icr terminals are sub-carriers that fall outside the set of sub-carriers occupied by the virtual carrier tenninals,. However if the schedulers for the virtual carrier and the host carrier are implemented. jointly, or have means to share information, then the scheduler of the host carrier can assign resource elements from within the virtual carrier region to tenninal devices on the host carrier during sub-frames when the virtual carrier scheduler indicates that some or all of the virtual carrier resources will not be used by terminal devices on the virtual carrier..

If a virtual carrier uplink incorporates a physical channel that follows a similar structure and method of operation to the LTE PUCCH, where resources for that physical channel are expected to be at the channel edges, for virtual carrier terminals these resources could be provided at the edges of the virtual carrier bandwidth and not at the edges of the host carrier. This is advantageous since it would ensure that virtual carrier uplinic transmissions remain within the reduced virtual carrier bandwidth..

Virtual Unlink Carrier Random Access hi accordance with conventional LTE techniques, it cannot be guaranteed that the PRACH will be within the sub-carriers allocated to the virtual carder In. some embodiments thexefore, the base station provides a secondary PRACH within the virtual uplink carder, the location of which can be signaled to the virtual carrier terminals via system information on the virtual carrier This is shown for example in Figure 13B in which a PRACH 1303 is located within the virtual carrier 1301. Thus, the virtual carrier terminals send PRACH. requests on the virtual carrier PRACH within the virtual uplink carrier. The position of the PRACH can be signaled to the virtual carder terminals in a virtual carder downlinlc signaling channel, for exampl.e in system information on the virtual carrier, However, in other examples, the virtual carrier PRACH 1303 is situated outside of the virtual carrier as shown for example in Figure 13C. This leaves more room within the virtual up]ink carrier for the transmission of data by the virtual carrier terminals. The position of the virtual carrier PRACH is signaled to the virtual carrier terminals as before but in order to transmit a random access request, the virtual carrier terminals re-tune their transmitter units to the virtual can-icr PRACH frequency because it is outside of the virtual carrier. The transmitter units are then re-timed to the virtual carrier frequency when uplin]c resource elements have been allocated.

In some examples where the virtual carrier terminals are capable of transmitting on a PRACH outside of the virtual can-icr, thìe position of the host carrier [BACH can he sialed to the virtual carrier terminals-The virtual carrier tenrìinals can then simply use the conventional host carrier PRACH resource to send random access requests This approach is advantsgeous as fewer PR.ACH resources have to be allocated.

However, if the base station is receiving random access requests from both conventional LTE terminals and virtual carrier terminals on the same FRACH resource, it is necessary that the base station is provided with a mechanism for distinguishing between random access requests from conventional [TB terminals and random access requests from virtual carrier terminals Therefore, in. some examples a time division allocation is implemented. at the base station whereby, -for example, over a first set of sub-frames the PRACH allocation is available to the virtual carrier terminals and over a second set of subframes the PEACH allocation is available tD conventional LIE terminals. Accordingly, the base station can determine that random access requests received during the fit-st set o-f sub-frames originate from virtual carrier-terminals and random access requests received during the second set of sub-frames originate from conventional LTE-terminals in other examples, no mechanism is provided to prevent both virtual carrier terminals and conventional LTB terminals transmitting random acceès requests at the same time..

However, the random access preambles that are conventionally used to transmit a-random access request are divided into two groups. The first group is used exclusively by virtual carrier tenninals and the second group is used exclusively by conventional LTE terminals.

Accordingly, the base station can determine whether a random request originated from a conventional LTE terminal or a virtual carrier terminal simply by ascertaining to what group the random access preamble belongs.

Figure 14 provides a schematic diagiarn showing part of an adapted LIE mobile telecommunication system arranged in accordance with an example of the present invention..

the system includes an adapted enhanced Node B (eNB) 1401 connected to a core network 1408 which conununicates data to a plurality of conventional LIE. tenninals 1402 and reduced capability terminals 1403 within a coverage area (cell) 1404. Each of the reduced capability terminals 140.3 has a transceiver unit 1 405 which includes a receiver unit capable of receiving data across a reduced bandwidth and a transmitter unit capable of transmitting data across a reduced bandwidth when compared with the capabilities of the transceiver units 1406 included i.n the conventional LTE terminals 1402.

The adapted eNB 1401 is arranged to transmit downlink data using a subfrarne structure that includes a virtual carrier as described with reference to Figure 5 and to receive uplink data using a sub-frame structure as described with refercnce to Figures 1,3B or 13C..

The reduced capability terminals 1403 are thus able to receive and transmit data using the uplink and downlink virtual carriers as described above..

As has been explained above, because the reduced complexity terminals 1403 receive and transmit data across a reduced bandwidth on the uplink and down]ink virtual carriers, the complexity, power consumption and cost of the transceiver unit 1405 needed to receive and decode downlink data and to encode and transmit uplinic data is reduced compared to the transceiver unit 1406 provided in the conventional LIE terminals When receiving downlink data from the core network 1408 to be transmitted to one of the terminals within the cell 1404, the adapted eNB 1401 is arranged to determine if the data is bound for a conven.bonal LTE terminal 1402 or a reduced capability terminal 1403. This can be achieved using any suitable technique.. For example, data bound for a reduced capability terminal J.403 may include a virtual carrier flag indicating that the data must be transmitted on the down]ink virtual carrier.. I the adapted eNB 1401 detects that downlin.k data is to be transmitted. to a. reduced capability terminal. 1403, sri adapted scheduling unit 1409 included in the adapted eNB 1401 ensures that the downliuk data is transmitted to the reduced capability terminal in question on the downlinlc virtual. In another exampl.e the network is arranged so that the virtual carrier i.s logically independent of the eNB. More particularly the virtual carrier may be arranged to appear to the core network as a distinct cell so that it is not known to the core network that the virtual carrier has any relationship with the host carrier Packets are simply routcd to/from the virtual carrier just as they would be for a conventional cell In another example, packet inspection is performed at a suitabie point within the network to route traffic to or from the appropriate carrier (i.e. the host carrier or the virtual carder) In yet another example, data from the core network to the eNf3 is communicated on a specific logical connection fbr a specific terminal device.. The eNB is provided with infonnation indicating which logical connection is associated with which terminal device.

Information is also provided at the eNB indicating which terminal devices are virtual carrier terminals and which are conventional LTE terminals. Tins information could be derived from the fact that a virtual carrier terminal would initially have connectcd using virtual carrier resources In other examples virtual can-icr terminals are arranged to indicate their capability to the eNl3 during the connection procedure.. Accordingly the eNB can map data from the core network to a specific terminal device based on whether the terminal device is a virtual carrier terminal or an LTE terminal.

When scheduling resources for the transmission of uplink data, the adapted eNB 1401 is arranged to determine if the terminal to be scheduled resources is a reduced capability terminal 1403 or a conventional LIE terminal 1 402. Tn sonic examples this i.s achieved by analysing the random access request transmitted on the PRACH using the techniques to distinguish between a virtual carrier random access request and a conventional random access request as descnbed above.. In any case, when it has been deternined at the adapted eNB 1401 that a random access request has been made by a reduced capabili' terminal 1402. the adapted scheduler 1409 is arranged to ensure that any grants of uplink resource elements are within the virtual uplink can-icr In some examples, the virtual carrier inserted within the host carrier ca.n be used to provide a logically distinct c1.1etFork within a network" In. other words data being transmitted via the virtual carrier can be treated as logically and physically distinct from the data transmitted by the host carrier network. The virtual carrier can therefore he used to implement a so-called dedicated messaging network (DivfN) which is "laid over" a conventional network and used to communicate messaging data to DMN devices (i.e. virtual carrier terminals).

Further Example Applications of Virtual Carriers Having set out the concepts of virtual carriers of the kind described in copending UK patent applications numbered GB 11019700 [2], GB 1101981.7 [3], GB 1101966.8 [4], GB 1101983.3 [5]. GB 1101853.8 [6], GB 1101982.5 [7], GB 1101980.9 [8] and GB 1101972.6 [9], some extensions oi the virtual carrier concept in accordance with embodiments of the invention are now described. In particular-, some implementations of virtual carrier concepts in the context of muiticast transmissions are described.

Before describing some example applications of the virtual carrier concept th th.e context of multicast transmissions, some general characteristics of frame structures for uplinic and duwnlink transmissions in an example telecommunications system implementing a virtual carrier in accordance with embodiments of the invention are summarised., Figure 15 is a schematic diagram representing how various regions in a LIE-type telecommunications network's tine-frequency uplinlc resource grid 1550 and dowalink resource grid 1500 might be allocated to support a virtual carrier such as described above. The upper grid 1550 in Figure 15 schematically represents the uplink resource allocation and the lower grid 1500 schematically represents the downlinlc resource allocation..

The extent of the example downlink resource grid 1500 shown in Figure 15 comprises ten sub-frames 1512 (equivalent to one frame overall) spaced along the horizontal time direction and spans a bandwidth R.320 in fi'equency, for example 20 MHz. As described above, the downlink transmission resource grid 1500 of Figure 15 comprises host carrier PDCCH regions 1502, host carrier P080-I regions 1506 and virtual can-icr regions 1510, The virtual carrier regions 1510 in this example comprise separate virtual carrier PDCCH regions 1514 and virtual carrier PDSCH regions 1516.. 1-lowever, and as noted above, in other example implementations the principles of the virtual, carrier operation might not mirror these aspects of LTE-type networks. The downlin,k frame sfructiire 1500 may include other regions, such as reference symbol regions, but these are not shown in Figure 15 for simplicity. Each sub-frame 1512 of the downlink. resource grid 1500 shown in Figure 15 broadly follows the same general format as the sub-frame shown in Figure 5, except in this particular example the virtual, carrier control region (VC-PDCCH) 1512 is positioned at the beginning of each sub- ñ-ame 1512, rather than at the end as schematically shown in Figure 5.

The extent of the uplink resource grid 1550 shown in Figure 1.5 also comprises ten sub-frames 1 562 (equivalent to one frame overall) spaced along the horizontal time direction and spanning the same bandwidth R320 in frequency.. The uplink transmission resource grid 1550 of Figure 15 comprises host carrier PUCCH regions 1552 (HC controJ regions), host canier PUSCH regions 1556, and virtual canier regions 1560 The respective virtual carrier regions]560 comprise virtual carrier PUCCH regions 1564 (VU control regions) and virtual carrier PTJSCH regions 1566. The uplink frame structure 1550 can include other regions, but these are again not shown in Figure 15 for simplicity.. Each sub-frame 1552 of the uplinic resource grid 1550 shown in Figure 15 may broadly follow the same general format as the suh-frarnes shown in Figures 1 3A to 13C, for example.

Hadng sununarised some aspects of uplink and downlink transmission resource grids in telecommunications systems implementing a virtual carrier in accordance with some embodiments of the invention, some applications of multicast techniques in such a system are now described.

Multicasting is an established technique used i.n various telecommunication systems, SLich as those operating in accordance with th.e general principles of the 3CiPP LTE standards.

Multicasting may be generally characterised as the simultaneous transmission of data. to multiple terminal devices which are members of a group defined fbr receiving the multicast data.. Multicast services may he contrasted with broadcast services and unicast services.. For example, broadcast services may be generally characterised by the ansmissiorj of data which can. be received by multiple terminal devices without the devices needing to be part of any particular defined sub-group of terminal devices. Unica.st services, on the other hand, may he generally characterised by die transmission of data intended for an individual terminal device with the data being specifically addressed to that terminal devict The inventors have recognized that multicasting maybe a particularly useflul mode for communicating data to machine-type coi-rmniunjcation terminal devices of the kind discussed above and which might frequently, though not exclusively, be associated with virtual can-iers,.

This is because in many situations it i.s expected there will be large numbers of machine-type communication terminals to which the same data is to be transmitted.. For example, a utilities provider may wish to communicate new pricing information or a sofl\vare update to all smart meters within a given communication cell, or a vending machine operator may wish to communicate new pricing information to vending machines configured as MTC devices (i.e having the ability to wirelessly communicate data with an MTC server using a wireless telecommunication system). Corresponding situations requiring the transmission of the same data to multiple terminal devices may arise in other circumstances, for example, with so-called smart grids and remote health care implementations of machine-type comiriunication networks / devices. Thus it is expected there will he many circumstances in wflich a virtual carrier of the kind discussed above may be employed to support multicast transmissions.

One example situation is schematically shown in Figure 16 which represents an architecture for a generally LIE-based telecommunications system 1600 implementing a rnulticast service in accordance with an embodiment of the invention. The system 1600 comprises an eNodeB (base station) 161 0 arranged to communicate with a plurality of terminal devices 1612 over a virtual carner of the kind described above. Although only one base station 1610 is shown in Figure 16 for simplicity, it will be appreciated that in general there will be multiple base stations to provide coverage for terminal devices over a range of different geographic locations (i.e. in different cells of the network)..

The terminal devices 1612 are communicatively coupled to associated "machines" 1614, which in the example shown in Figure 16 are vending machines 1614.. Thus the terminal devices 1612 provide a means for the vending machines to communicate, via the base station 1610, with a remote MTC server (not shown) through the telecommunications network 1600.. As is conventional, the base station 1610 may comprise a transceiver unit 161 Oa for transmission and reception of wireless signals and a controller unit 161Db conflgl]red to control the base station 161.0 to operate as desired according to the principles described herein, As is also conventional, the terminal devices 1612 may each comprise a transceiver unit 1.6l2a for transmission and reception of wireless signals and a controller unit 16 12b configured to control the respective terminal devices 1612 to operate as desired according to the principles described herein. For example, the respective controller units 161Db, 1612b may comprise respective processor units which are suitably configured / programmed to provide the desired functionality using conventional programming / configuration techniques for equiprnen.t in wireless telecommunications systems.

The terminal devices 1.612 are schematically represented in Figure 16 as receiving a niultieast communication from the base station 1610 indicating an increase in price should be applied for' the associated vending machines.. That is to say the terminal devices 1612 (perhaps along with oilier terminal devices in other cells served by other base stations) form a m'ulticast group and the "price up" communication schematically represented iii Figure 16 may be addressed to this muiticast c'up in accordance with the established general principles of multicasting, e.g. based on multicast group 1D addressing. The "price up" communication fin may he instigated by a remote MIC server responsible for managing the operation of tile network of vending machines 1614 and routed to the base station 1610 for niulticast transmission to the terminal devices 1612 in. accordance vith generally conventional.

techniques. EurO enuore, the terminal devices 1612 receivtng the "price-up" multicast communication may he configured to extract the relevant information from the multicast communication and pass the infOrmation to l:h.eir associated vending machine 1614, which may react accordingly, again using generally conventional techniques.

A potential advantage of using a multicast approach to communicate the price-up message to the terminal devices 1612 shown in Figure 16, as compared to a unicast approach to each individual terminal device, is reduced signalling overhead, This can be the case both in terms of control-plane signalling (e.g. on the virtual carrier PDCC.H 1514 shown in Figure 15) and in terms of user-plane signalling (e.g. on the virrual carrier PDSCH shown in Figure 15). With a large number of terminal devices in a cell, the amount of control and userp1ane signalling to transfer MTC messages in a unicast manner to each individual terminal device could easily come to dominate the total available resources, making the system inefficient, and perhaps even unfeasible.. Control-plane signalling may in particular become overloaded because the actual user-plane data to be communicated, e.g. a simple indication of a price increase, might in itself be relatively small.

Using multicast techniques to communicate data to multiple terminal devices can thus help reduce the amount of control signalling overhead. However, a drawback of current techniques for multicast transmissions, for example as defined in the relevan.t existing LTE standards, is a lack of a mechanism fot terminal devices to acknowledge receipt of the transmission.. This is because multicast services are unidirectional services. The present inventors have recognized this aspect of existing multicast schemes can have a detrimental impact in many situations, and in particular for some MTC applications, such as the vending machine example' of' Figure 16. For example, it might be problematic if not all the vending machines 1614 successfully receive new pricing information bccause sonic of the machines will be chaiging the wrong price(s). Using current multic.ast techniques, an MTC server responsible for managing the networlc of vending machines 1614 would not he able to determine whether or not the respective vending machines have successfully received any given multicast transmission.. Because of this the MTC server cannot lcnow if corrective action (e.g. re-transmission of data) is required.

I

Telecommunications systems generally provide a mechanism for terminal devices to acknowledge correct receipt of unicast communications / packets, e.g. based on ACK / NACK.

signalling according to a defined ARQ (automatic repeat request) / i-IARQ (hybrid automatic repeat request) procedure. LIE, fbi example, employs a i-1ARQ procedure a.s described in ETSI iS 136 213 V102.0(20i1-06)/3GPP iS 36.213 version 10.2.0 Release 10) F10 and ETSI is 1.36 321 V10.2..0 (2011-06) / 30PP IS 36.321 version 10.2.0 Release 10) [11].

Figure 1 7A schematically represents how the uplink and clownlink transmissions resources represented in Figure 15 might be used to provide for a F.ARQ procedure for a virtual carrier in a unicast context. The various elements of Figure 1 7A will be understood from the above description of the corresponding elements in Figure 15. in general, the HARQ procedure may operate in the same general way as for a conventional (Le. non-virtual) carder, That is to say it may operate by following the principles of conventional HARQ techniques in the telecommunications system in which the virtual carrier is implemented. in this example it is assumed the telecommunications system is a generally LTE compliant system.. Thus downlinic data received by a terminal device on the virtual carrier's PDSCH 1516 in sub-frame i are acknowledged I negative acknowledged by an uplink ACK. / NACK signal sent on the virtual carrier's PIJOCH 1564 in sub-frame i+4.. This is schematically shown in Figure HA by three uplink ACK / NACK signal responses 1710, 1720, 1730 associated with respective downlink data transmissions 1112, 1722, 1732 from four sub-frames earlier.. As with conventional LTE ACK / NACK. pit eedurts, ACK I NACK signalling may also be sent on PUS'CFI, for example, when a terminal device is allocated uplink resources for user-plane data on PIJSCH in the same sub-frame as the ACK / NACIC response.

Figure 1 7B schematically represents how uplink PUCCU resources 1564 might be allocated for a virtual carrier operating in accordance with an embodiment of the invention..

Th.e region of the uplink transmission resource grid shown in Figure l7B corresponds to a single sub-frame of' the uplinic transmission resource grid 1550 shown in Figure 15 for a bandwidth corresponding to the extent of the virtual carrier. It is assumed for this example that the virtual carrier PUCCHI resource allocation broadly follows the same principles as for a conventional LTE carrier-Thus resources are allocated in pairs towards the upper and lower frequcncy boundaries / edges for the virtual carrier. hi the example shown in Figure l7B the resources associated with respective paiñngs are indicated by the same letter A., B, C, D, B or F. In the example shown in Figure 17B there are enough PUCCH resources for 36 transmissions pci sub-frame, The inventors have recognized that these different resources can be used by different terminal devices to send an ACK. / NACK in response to a multicast transmission Thus some embodiments of the invention provide a method for communicating data in a wii-eless telccommun.cations system which comprises transmitting a multicast transmission from a base station to a plurality of terminal devices and receiving response signals from respective ones of the terminal devices to indicate whether or not the respective terminal devices have successthlly received the multicast transmission. Furthermore, this may be done using a virtual carrier of the kind described above within the operating bandwidth of a host carrier This provides a mechanism for a MTC server, for example, to instigate the transmission of multicast data to a plurality of associated MIC devices, and to receive feedback via Ih.e base station regarding the extent to which the transmission has been received by the intended recipients.. For example, th.e base station ma.y fonvard information regarding individual response signals to the MTC server, or may simply send a message to the MIt server to indicate! whether or not all the intended recipient terminals received the! multicast transmission. The MIC server may then decide on the appropriate course of action! For example, if the MTC server is informed by the base station that there!! is at least one MTC device which did not successfiuily receive the inulticast transmission, the M'I'C server may decide to instigate a re-transmission immediately, or at a later stage, or determine that the transmission was noncritical and take no action.

Tn other examples the MTC server might not play a role in the feedback mechanism provided by the response signals and this might he managed solely by the telecommunications network, fbr example, within the respective base station(s). That is to say, the base station(s) may be configured to receive the response signals, determine which (If any) intended recipient devices within their area have not acknowledged successfiul reception of the multicast tnnsmission (for' example, because they have not responded or responded with a negative acknowledgement), and take action to re-transmit the data as appropriate. The base station(s) may detennine different re-transmission strategies depending on the number! of terminal devices they arc serving which, do not indicate successfrtl reception For example, if there are many failed receptions within a base station's eel], re-transmission by way of another multicast may be considered appropriate!! However, if there are only one or a few failed receptions, a unicast transmission scheme for each individual terminal devices not reporting succcssftl reception may be considered more appropriateS Figure I SA schematically represents how the uplink and downlink transmissions resources represented in Figure 1 5 might be used to provide for a HARQ procedure For a virtual can-icr in a multicast context in accordance with an embodiment of the invention. The vanous elements of Figure ISA will be understood from the above description of the corresponding elements in Figure 15 Thus Figure ISA schematically s]lows three multicast transmissions 1812, 1822, 1832 occurring on PDSCH in different sub-frames of the downlink radio frame represented in the figure. These multicast transmissions may be based on conventional techniques and identify the intended recipients by virtue of a multicast group ID in the normal way. The three different transmissions shown in Figure 1 SA may be urn-elated fi-om on.e another (e.g., independent transmissions intended for different multicast groups), or may be related, ag. s series of transmissions for! the same multicast group. The specific nature of the information being transmitted is not significant to the underlying operating principles.

In accordance with embodiments of the invention, terminal devices which are members of a mul.ticast group to which a transmission is made are configured to send an acknowledgement / negative acknowledgment (ACK. / NACIC) in response to the multicast transmission.. The configuration of these multicast ACIC / NACK response signals may follow the same general principles, e.g. in terms of signalling format and content, as for conventional ACIC / NACK signalling associated with conventional unicast transmission schemes.

Furthermore, and as with Figure l7A, the muhicast ACK / NACK. responses sent in response to a. multicast transmission in a virtual carrier context may be sent on a PUCCH 1564 associated with the virtual carrier., in accordance with existing LTE standards for ACIC / NACK signalling in a uni cast context, an ACIC /NACJC response signal is sent by a terminal device (user equipment -TIE) in a sub-frame which i.s four sub--frames later than the sub-frame i.n which the corresponding d.ownlinlc transmission is scheduled on PDSCFJ. Scheduling information (resource allocation) for downlink transmissions is cairied on PDCCH, and for conventional unicast ACK / NACK. signalling, the particular uplink transmission resource on PLJCCH. which is used for the ACK / NACK. signalling is based on the PDCCH resources used to allocate the downlink transmission, However, in a multicast context, different uplink transmission resources (e.g. in terms of times and/or frequencies and/or codes) may be used for ACK. I NACIC signalling from diffcrent terminal devices to allow tile response signals to be distinguished at the base station.

For example, based on the uplinlc sub-frame stnicture shown iii Figures 1 7B and the us-c of vitual carrier PUCCH for ACK / NACK signalling, 36 different terminal devices might be configured to use different ones of the 36 available PUOCH resources in a sub-frame which is four sub-frames later than the sub-frame in which the multicast data is transmitted,. This is the approach schematically -epresented in Figure 1 8A by the three PUCCFI regions 1810, 1820.

1830 each containing (up to) 36 ACK/NACK signals in sub-flames rhich are four later than the respective corresponding multicast t.ranEmlissions 1812, 1822, 1832. The different termjnal devices may be allocated the specific resources to use for their respective ACK / NACK signalling during an initial set-up procedure. For example, the different tenninal devices might he provided with information regarding the specific PUCCI-1 resource to use within each sub-frame when being allocated a CRNTJ.. In other examples, additional signalling associated with a multicast transmission may be used by the base station to allocate specific PUCCH resource for ACK / NACK. response signals to each terminal device.. Thus there are a number of ways in which the respective base station(s) can manage the different uplink resources to be used for ACK / NACK signalling by different terminal devices within the different multicast groups to allow received ACK I NACK responses l.o be mapped to corresponding terminal devices.

For a conventional ACK / NACK procedure in a unicast conteict the specific PUCCH resource to be used for the ACK I NACIC response within the iclevant sub-frame (e.g. four sub-frames later than the downlinlc transmission) can he derived by the tetminal device in different ways. For example, with dynamic downlinlc scheduling the specific P'UCHH resource to use when sending an ACE. / NACK response is implicitly signafled by the allocation message on PDCCH for the PDSCH data transmission that is to be AClCed / NACKed. Alternatively, with semi-persistent scheduling there will not necessarily he corresponding PDCCH allocation data for the down]ink transmissions, and in this case the specific PUCCE resource to use within the relevant sub-frame (e.g thur sub-frames later than the downlinlc) may be predefined as a part of the procedure for' setting up the downlink transmission.

In a multicast context there are also a number of different ways in which the specific PUCCH resource to use by the respective terminal, devices can be establisheth F or example, the eNodeB may provide an indiathon through additional signalling on PDCCH or FDSCH in association with the multicast downhnk transmission toni which the respective terminal devices can derive their own PUCHH resource For example, the eNodeB may transmit information linking specific identifiers [or the different terminal devices that arc members of the mu]ticast group within the sNodeB's footprint (e.g.. radio-network temporary identifiers -R.NTIs) with specific PUCCH uplink resources (or indeed any other uplink resources) to be used for ACK / NACK. signalling by the colTesponding terminal device., The various terminal devices can thus receive this information, identify their specific identifier from among the other members of the multicast group, and determine the appropriate uplink resource accordingly. The uplink resource indication may, for example, specify a particular resource within a sub-frame and a particular sub-frame to use, or may simply specify a particular resource within to be used in a default sub-frame, for example, a sub-frame that is four sub-frames later than a sub-frame in which the corresponding multicast transmission is made..

1 5 In other examples, the specific resource to be used by a given terminal device for ACK. I NACK. signalling may be established during a set up procedure.. For example, when a terminal device that is a m..ember of a multieast -oup for which ACK / NACIC signalling is to be used in accordance with an embodiment of the invention first connects to the eNodeB, or when a multicast transmission first begins.

Figure 18B is a signalling ladder diagram showing how a base station (eNodeB) 1850 may communicate ACK. I NACIK signalling resource information (i.e. information on which uplink resource to use for ACK / NACK signalling) to different terminal devices (UBs), such as UE X (identified by reference number 1860) and UF V (identified by reference number 1 870) which are both subscribers to the same muiticast service "A"..

th the example of Figure 183, the ACK. / NACIK. signalling resource information is defined during an initial set up stage when terminal devices connect to the network. Thus, UF X, upon waking up, for example, sends a random access preamble to the eNodeB, in order to be recognized by the eNodeB., After a. Random Access handshake procedure, RRC signalling is exchanged, and the terminal device 1860 (UE X is allocated a C-R}TJ (Cell Radio Network Temporary Identity) by the eNodeB. The C-RNTI is an address which is used to identify the UE in communications with the eNodeB, fri the example of Figure 18B it i.e assumed UE X is allocated a C-RNTI of"X". In this sequence, along with the UB-specific C RNTI assignment. a Group C-R.NTI associated with the mullicast group is also communicated to the [iF. In the example of Figure 1313 it is assumed the relevant multicast service is associated with a Group C-RNTI of "A". This prOCeSS of allocating C-RNTIs may be generally performed in accordance with known techniques However, in addition to allocating ftc two types of C-RNTI, the eNodeB also allocates liE X an AC1C / NACK signalling resource to be used by the LIE when determining the specific uplink. resource for ACK. / NACK signalling in response to multicast transmissions addressed to the niulticast Group C-RNTI of "A". In the example of Figure 1313 it is assumed UP X is allocated un ACK. / NACIC signalling resource infomntion "M", where "M" eon-esponds to (i.e. identifies) a specific PUCCIl resource within sub-frames of the virtual carrier in which the scheme is implemented The set-up signalling associated with allocating liE X with C-RNTI "X". Group C-R.NTI "A", and ACK / NACK signalling resource information "M", is schematically represented in Figure 1813 by reference numeral 1880.

Similar set-up signalling (schematically represented in Figure 1313 by reference numeral 1832) is provided for the terminal device 1870 (UP Y). Thus, UP Y, upon waldng up, for example, sends a random access preamble to fte eNoc]eB, in order to he recognized by the eNodeB. After a Random Access handshake procedure, RRC signalling is exchanged, and the terminal device 1870 (UP Y) is allocated a C-RNTJ by the eNodcB, The C-RNTI is an address which is used to identify the UP Y in communication with the eNodeB, In the example of Figure 1 SB it is assumed UP. Y is allocated a C-RNTI of "Y". In this sequence, along with the UP-specific C-RNTI assignment, a Group C-RNTI associated with the multieast group is also communicated to the UP.. In the example of Figure 1813 the relevant muiticast sen'ice is associated with a Group C-RNTI of "&" As for UP X, in addition to allocating the two types of C-RNTI for UP Y, the eNodeB also allocates LIE Y an ACIC / NACK. signalling resource to he used by LIE Y when determining the specific uplin.k resource for ACK / NACIC signalling in response to multicast transmissions addressed to the multicast Group C-PJ'411 of"A". In the example of Figure 1SB it is assumcd UP Y is allocated an ACK I NACK signalling resource information "N", where tJ" identifies a specific PUCCH resource within sub-frames of the virtual carrier which is different fiom that indicated by ACK. I NACJ( signalling resource information "M" for UP N...

Subsequently a downlinlc multicast transmission 1 884 addressed to a multicast oup ID corresponding to Group C-RNTI "A" s made.. This may he instigated by a remote MTC server associated with the terminal devices UE X and UB Y and promulgated thraugh the network to the eNodeB 1850 for transmission in the normal way.

The terminal devices LiE X and UI,.. Y are aware the multicast transmission is intended for them based on the Group C-RNT1 = "A" in the normal way Thus each terminal device seeks to receive and process the transmission, and in accordance with the above-described pi-in.ciples of embodiments of the invention, the terminal devices addressed by the multicast -ansrnission are configured to send an uplith. ACK I NACIC signal in response. As schematically represented in Figure l8A, it is assumed in this example the terminal devices are configured to respond with appropriate ACIC I NACK signalling in a sub-frame which is four sub-flames later than that containing the multicast transmission 1884 (Le.. following the same general timing as for unicast ACK / NACK. signalling).. Furthermore, the different tiEs 1860, 1870 are configured to use diffeTent P'UCCH resources for their respective ACK I NACK. signalling according to the respective ACJK. I NACK. signalling resource indications they received during set up. Thus in this example, UE X 1860 sends an ACK. I NACK response in the relevant sub-frame on a PUCCH resource identified by ACK. / NACK signalling resource indication EM" (schematically indicted in Figure 1 SB by signalling 1886); and UE Y 1870 sends an ACIC / NACIC response in the relevant sub-frame on a PUCCH resource identified by ACK. I NACK. signalling resource indication "N" (schematically indicted in Figure 18B by signalling 1888). The specific format for the ACK / NACK.

response signals 1886, 1888 is not significant and can. be arranged in accordance with any desued scheme, for example it may simply follow the same general principles as for established ACIC / NA.CK. response signalling associated with unicast fransmissions.

Thus Figure ISB shows one example scheme by which an eNodeB 1600, 1850 can allocate different PUCCH resources to different terminal devices subscribing to a given multicast service to manage the different uplinic resources used by the different terminal devices for ACK / NACK response signalling-Alternate schemes may be used in other examples For example, in some cases ACK I NACIC signalling resource indications may not be explicitly communicated to different terminal device during a set-up procedure, but may be communicated implicitly instead, for example within, the specific C-RNTI allocated by the eNodeB. For example, an eNodeB might i.n effect reserve a series of C-RNTI values to be allocated to terminal devices within a given multicast group whereby a characteristic of the C-RNTI may be used to indicate which uplirdc resource should he used by Ihe respective terrcnnal devices For example, an eNodeB may allocate 04±411 values fi-om a series for which some of the digits, for example the last fbw bits, colTespond to a different number for each terminal device, and based on which each terminal device derives n appropriate uplinic PUCCH resource for! ACK / NACK signalling. In principle, different terminal devices within a given multicast group could each he configured to use particular uplink resources without network signalling, for example, the information could be in effect be hardwired in the terminal device, for example during manufacture or deployment. This approach is perhaps less flexible. hut may nonetheless be appropriate in some cases, for example, where it is know there will be little or changes to the multicast group members for an. extended time., in some cases there may he fewer than 36 PUCCI-I resources available in a given sub-flame (e.g.. because of poor channel conditions), and even if there are 36 P1DCCH r-esources available for ACK / NACK. signalling, there might he more than 36 terminal devices receiving the multicast transmission.. in cases such as this where there may be more ACK. / NACK response signals than available PUCCU resources per sub-frame, the system may be configured to use additional resources, for example, PUCCH resources in additional sub-flames, PUCCH resources on additional virtual carriers, or other resources elsewhere in the uplink frequency resource grid (for example, on a virtual carrier's PUSCH).

In this regard the temiina] devices of a multicast grdup might be notionally separated into sub-groups with each sub-group containing a number of tenninal devices for which ACK / NACK signalling can he accommodated on PUCCE. in a single sub-frame, For example, assuming there are 36 PUCCH resources available in each sub-flame, and there are, say, 60 terminal devices in a given multicast group, 36 of the devices might be allocated to a first sub-group (Sub-group I) while the remaining 24 terminal dcvice might be allocated to a secon.d sub-group (Sub-group II). Of course if the there are still more terminal devices in a nmlticst group, there may be more notional sub-groups defined.. The resources to be used by the different tenninal devices for ACI<. / NACK response signalling may then be configured differently for the different sub-groups. For example, the different sub-groups may be configured to respond in different sub-frames or on different virtual carriers.

Figure 19 schematically represents how uplink and downlink transmission resources might be used to provide for a HARQ procedure for a virtual carder in a multicast context in accordance. with an embodiment of the invention when there are more recipient terminal devices than there rn-c available PUCCH resources for ACK / NACK responses in each sub-frame of a virtual carrier.. \Jarious elements of Figure 19 will be understood from the description of corresponding elements in j:igures 1.5 and 18 in the example shown here it is assumed PUCCH is able to support 36 ACK I NACK. response siguals from separate terminal devices in each sub-frame, but there are somewhere between 37 and 72 terminal devices receiving the multicast transmission. Thus the terminal devices are notionally divided in to iwo sub-groups such as described above.. The sub-groups may be referred to here as Sub-group I and Sub-group II, and in this example it is assumed the temiinai devices are aware of which sub-group they are in. There are various ways of communicating the relevant sub-group information (information indicative of the relevant notional sub-group) to the different terminal devices, as described further below.

In accordance with the scheme shown in Figure 1 9 terminal devices in different sub-groups are operable to send ACK / NACK response signals in different sub-flames, This allows the base station to receive more 1-esponses than can be accommodated within a single sub-frame. Thus in this particular example, in response to a multicast transmission 1912, Sub-group I terminal devices are configured to send their ACK. I NACK signals four sub-frames later using PUCCIl resources 1910 and Sub-group II terminal devices ale configured to send their ACK / NACIK.. signals five sub-frames later using PUCCI-I resources 1920. Thus a base station is able to in effect group terminal devices which ale members of a given multieast oup into sub-groups for the purpose of assigning uplink resources to be used by the tenninal devices for ACK / NACK signalling.

Figure 20 schematically represents how uplink and downiink transmission resources might be used to provide for a RARQ procedure for a virtual carder in a multieast context in accordance with another embodiment of the invention when there are more recipient terminal devices than there are available PUCCH resources for ACK / NACK. responses in each sub-frame of a virtual carrier. Various elements of Figure 20 will be understood from the description of corresponding elements in. Figures 15 and 18. However, whereas in Figures 15 and 1 8 a single virtual carrier is provided within a host carrier bandwidth, in the example of Figure 20 there are two separate virtual carriers (VCI & VC2) defined for the purposes of resource allocation. The two virtual carriers may be configured in the same way as one another, and each one may in turn he defined in the same was as any of the single virtual caniei examples described above. with the oniy diffdrence being the diff&rent operating fiequencies allocated to each virtual carrier (ic. the specific OFDM sub-ean-ie]-s).

In the example shown here it is assu med that each PUCCH (1564, 1564') is able to support 36 ACK / NA.CK response signals from separate terminal devices in each sub-frame, but there are again somewhere between 37 and 72 terminal devices receiving a rnulticast transmission on the first virtual carrier VC1. As before, the terminal devices are notionally divided in to two sub-groups, which may again, be referred to here as Sub-group I and Sub-group II.

In accordance with the schcme shown in Figure 20 terminal devices in different sub-groups are operable to send ACK I NACK response signals in the sainc sub-frames, but using different virtual carriers., This allows the base station to receive more responses than can be accomniodaled withi.n a single sub-frame of a single virtual carrier.. Thus in this pathcular example] in response to a rnultieast transmission 201.2, Sub-group I terminal devices are configured to send their ACK I NACIC signals four sub-frames later using PUCCII resources 2010 on virtual canier VCI while Sub-group II terminal devices are configured to send their ACK. / NACK signals in the corresponding sub-frame using PUCCJTI resources 2020 on virtual carrier VC2. This provides another mechanism whereby a base station is abl.e to group terminal devices which are members of a. multicast group into sub-gror.ips for the purpose of a.ssigrung different uplinic resources to be used by the terminal devices for ACK I NACK: signalling.

Figure 21 is a signalling ladder diagram showing how a base station (eNodefl) .2100 might communicate sub-grouping information to different terminal devices (UPs), such as UP X (identified by reference number 2110) and UP Y (identified by reference number 2120) which are both subscribers to the same multicast service "A".

In the example of Figure 2.1, the sub-groups are defined during an initial set up sta2e when terminal devices connect to the network, Thus, UP. X, upon waking up, for example.

sends a. random access preamble to the eNodeP, in order to be recognized by the eNodeB.

After a Random Access handshake procedure, RRC signalling is exchanged, and the terminal device 2110 (UP X) is allocated a C-RNTI (Cell Radio Network Temporary Identity) by the eNodeB The C-RNTI is an address which is used to identify the HE in communication with the eNodeB. In the example of Figure 21 it is assumed TIE X is allocated a C-RNTI of "X". In this sequence, along with the UP-specific C-RNTI assignment, a Group C-RNTI associated with the multicast group is also communicated to the UE In the example of Figure 21 it is assumed the relevant multicast serwice is associated with a Group C-RNTI of "A". This process of allocating C-RNTIs may he generally performed in accordance with known techniques.. However, in addition to allocating the two types of C-RNTT, the eNodeB also S allocates TiE X a multicast subg oup ID to be used by the TiE when detenni.ning the resources fhr ACIC / NACK.. signalling in response to multicast transmissions addressed to the multieast Group C-Rl'JTI of*"A".. In the example of Figure 21 it is assumed TiE X is al]ocated to multica.st subgroup TD "" It will be appreciated i.n some examples TiE X may also be provided with an indication 1 0 at this stage as to which PUCCH resource in a given sub-frame the TIE. should use for ACK / NACIC signalling, such as shown in Figure 1 SB However, this is not represented in Figure 21 (or in Fignre 22 below) fbr simplicity.

The set-up signalling associated with allocating UE X with C-R.NTl "X", Group C-RNTI "A", and subgroup ID "I", is schematically represented in Figure 21 by reference numeral 2130.

Similar set-up signalling (schematically represented in Figure 21 by reference numeral 2140) is provided for the terminal device 2120 (lIE Y). Thus, LIE Y, upon waking up, for example, sends a random access preamble to the eNodeB, in order to be recognized by the eNodeB. After a Random Access handshake procedure, RRC signalling is exchanged, and the terminal device 2120 (UB Y) is allocated a C-RNTI by the eNodeB. The C-RNTI is an address which is used to identify the TIE Y in communication with the eNodeB. In the example of Figure 21 it is assumed UE Y is allocated a C-RNTI of "Y".. In this sequence, along with the UF-specific C-RNTJ assignment, a Group C-lthTI associated with the multicast group is also communicated to the TiE. In the example of Figure 21 the relevant multicast seivice is associated with a Group C-RNT1 of "A".. In addition to allocating the two types of C-R.NT1, the eNodeB also allocates TiE Y a multicast subgroup ID to be used by the TIE when determining the resources for ACIC / NACK signalling in response to multicast transinission.s addressed to the multicast Group C-RNTI of "A" In the example of Figure 21 it is assumed TIE Y is allocated to inulticast subgroup ID "IT".

Subsequently a downlink irnilticast transmission 2150 addressed to a multicast group ID corresponding to Group C-RNTI = "A" is made. This may be instigated by a remote MIC server associated with the terminal devices UE X and UF Y and promulgated through the fletwork to the eNodeB 2100 fbi transmission in the normal way.

T]ie temiinai devices UB X and UE Y are aware the multica.st transmission is intended for them based on the Group C-R.NTJ "A" in the normal way. Thus each tenninal device seeks to receive and process the transmission, and in accordance with the above-described principles of embodiments of the invention, the terminal devices addressed by the multicast transmission are configured to send an uplink ACK / NACIC signal in!esponse. In this example, it is assumed the terminal devices are configured such that if they are associated with a multicast subgroup ID "1", they send their ACIC / NACK response after a first time has elapsed (schematically indicted in Figure 21 by signalhng 2160), and if they are associated with a multicast subgroup ID "11", they send their ACK I NACIC response after a second time, which is different from the fiist time, has elapsed (schematically indicted in Figure 21 by signalling 2170). For example, the HARQ timing for terminal devices which have been allocated by the eNode[3 to multicast subgroup ID l" might be such that the terminal device UF X responds with ACIC / NACK signalling in a subflame which is four sub-frames later than the downlink multicast transmission (e.g. such as identified by reference numeral 191.0 in Figure 19). The I-IARQ timing for tenninal devices which have been allocated by the eNodeB to multicast subgroup ID "H" might then be such that the terminal device UE Y responds with ACK / NACK signalling in a sub-frame which is live sub-frames later than the downiinl< niulticast transmission (e.g. such as identified by reference numeral 1920 in Figure 19).

As explained above with reference to Figure 20, in some implementations different sub-groups might be associated with AC1C / NACK. response signalling on different carriers instead of (or in addition to) ACIC / NACK signalling in different sub-flames as in Figure 19.

For example, the I-IARQ response for terminal devices which have been allocated by the eNodeB to multicast subgroup B) "I" might be such that the terminal device responds with ACIC / NACIC. signalling on a first virtual carrier in a sub-frame which is four sub-frames later than the downuin]c muiticast transmission (e.g. such as identified by reference numeral 201.0 in Figure 20). Terminal devices which have been allocated by the eNodeu to multicast subgroup ID "IT" might then be configured such that the terminal device responds with ACK I NACIC signalling on a second virtual carrier in a sub-flame which is four sub-frames later than the downlink multicast transmission (e.g. such as identified by reference numeral 2020 in Figure 20).

Thus Figure 21 shows one example scheme by which an eNodeB 1600 can allocate different teni-iinal devices subscribing to a given multicast service to different sub-groups to manage the uplinlc resources used by diffrent terminal devices for ACK I NACK response signalling.

Figure 22 is a signalling ladder diagram showing how a base station (eNodeB) 2200 might communicate sub-grouping information to different terminal devices (TiEs), such as UF.

X (identified. by reference number 2210) and UF Y (identified by reference number 2220) which are both subscribers to the same multicast service "A" according to another embodiment of the invention. This differs from the scheme of Figure 21 in that sub-group information is not communicated to terminal devices during set up.

Thus, TiE X 2210, upon waking up, for example, obtains a C-RNTI and multicast Group C-RNTI from the eNodeB 2200 in the same general maimer as in Figure 21 and in accordance with established techniques.. As with Figure 21, in the example of Figure 22 it is assumed TiE. X is allocated a C-R.NTI of "X" and. is provided with a multieast Group C-RNTI of "A't. The set-up signalling associated with allocating TiE X with C-RI4TI "X" and Group C-RNTI "A" is schematically represented in Figure 22 by reference numeral 2230..

Similar set-up signalling (schematically represented in Figure 22 by reference numeral 2240) is provided for the terminal device 2220 (TiE Y).. Thus, TiE Y, upon waking up, obtains a C-RNTI "Y" and a multicast Group C-RNTI "A" from the eNodeB 2200.

Subsequently a downlink multicast transmission 2250 addressed to a mullicast group ID corresponding to Group C-RNIJ = "A" is made. This may be instigated by a remote MTC server associated with the terminal devices UE X and TiE Y and promulgated through the network to the eNode'13 2100 for transmission in the normal way. In accordance with this example embodiment the present invention, the eNodeB 2200 is configured to determine how many sub-groups are needed to ensure the total number of ACK / NACK responses expected from terminal devices subscribed to multicast service "A" within the eNodeB's cell range can be accommodated., For example, if up to.36 ACK / NACK. responses can be accommodated in a single sub-frame, and there are N terminal devices subscribed to multicast service "A" within the eNodeB's cell range, it may be appropriate to divide the N terminal devices into n subgroups, where n = CEILING(N136).

The eNodeB may then be configured to communicate the value n in association with the downlink multicast transmission 2250 (e g. in an additional. PDCCH field). Terminal devices may then detennine an appropriate resource for their ACM. / NACIC response brised on n and their C-Ri' Ti. For example, individual terminal devices may determine their own sub-group ID by determining the value of (C-RNTI mod n).. Assuming the C-RNTI values allocated by eNodeB to the various lEa are suitably distributed, this process will ensure the terminal devices will in effect selforga.nise into u.n appropriate number of subgroups. If the C-RFTT values are not uniformly distributed (e.g. if there are more even-numbered C-R.NTI values allocated to subscribers of multicast service than odd-numbered C-R}4T1 values), the eNodeB can take account of this and increase n accordingly -tha.t is to say, the eNodeB can "over segnient" the group to ensure no sub-group has more than 36 membeis. Be cause the eNodeB lcnows exactly what C-RNTIs have been allocated, it can determine how large n should he to ensure there are no subgroups with more members than desired..

In the example of Figure 22, it is assumed there are only two sub-groups required to manage the available resources for ACK / NACIC signalling, thus each terminal device determines a HIARQ timing based on the value of (C-R.NTI mod 2).

is The terminal devices UP X and UE Y are aware the multicast transmission 2250 is intended for them based on the Group C-RNTI "A" in the nonnal way. The UEs 2210, 2220 also determine their sub-group ID from the value of n signalled by the eNodeB 2200 (in this example n zz. 2). Here it assumed C-RNTI "X" mod 2 0, which is taken as corresponding to a. multicast subgroup ID "I", and C-RNTI "Y" mod 2 = 1, which is taken as corresponding to a multieast subgroup ID "II".

Each teiminal device seeks to receive and process the transmission, and in accordance with the above-described principles of embodiments of the invention, the temñnal devices addressed by the multicast transmission are configured to send an uplink ACK. / NACK signal in response. In this example, it is assumed the terminal devices are configured such that if they are associated with a multicast subgroup ID"l", they send theft LACK. I NACK. response after a first time has elapsed (schematically indicted in Figure 22 by signalling 2260), and if they are associated with a mixiticast subgroup i'D "H". they send their ACK / NACIC response afler a second time, which is different from the first time, has elapsed (schematically indicted in Figure 22 by signalling 2270), For example, the HARQ timing for terminal devices in multieast subgroup ID "I" might be such that the terminal device TiE X responds with ACK / NACIC signalling in a sub-flame which is four sub-frames later than the downlinlc multicast transmission (e.g.. such as identified by reference numeral 1910 in Figure 19). The HARQ timing for tenninal devices in urulticast subgroup ID "II" might then be such that the tenni.nal device HE 1 responds with ACK / NACK. signalling in a sub-frame which is live sub-frames later than the downlinlc multicast transmission (eg. such as identified by reference numeral 1920 in Figure 1 9) S Again as explained above with reference to Figure 20, in some implementations different sub-groups might be associated with ACK. I NACK response signalling on different carriers instead of (or in addition to) ACIC / NACIC signalling in different sub-frames as in Figure 19.

In another example for handling more ACIC / NACK responses than can I 0 accommodated in a single sub-frame, the nmlticast group itself may in effect he split into several smaller muiticast groups having different multicast group IDs and each containing a number of terminal devices that can send an ACIC I NACK.. response in the same sub-frame. A multicast transmission intended for all the terminal devices i.n the multicast group may thcn be transmitted as separate multicast transmissions separately for each of the subgroups using the coi-responding multica.st IDs. Terminal devices within each sub-group can then respond in the manner described above with reference to Figure 1 8A to the muiticast transmission addressed to their multicast (sub-)group ID.. This has the advantage of allowing all ACK. / NACK.

rcsponses to he received in a given sub-frame following a multicast transmission, hut relies on multiple transmissions of multicast data (because it is repeated for each multicast sub-group).

It will be further be appreciated that the principles described above in relation to Figures 1 9 to 22 regarding mechanisms for managing ACK / NACK response signalling in more than one sub-frame of one virtual carrier may be combined with any of the principles described above for managing ACK I NACK response sigualling within any given sub-frame, for example as described with reference to Figure 18W Thus a base station (eNodeB) is able to manage which uplink resource are to be used by different terminal devices (liEs) which are members of a given multicast group based on two parameters, namely an indication of which resource to use with the subframe structure, and an indication of which sub-frame to use.

This two-parameter addressing mechanism can he an efficient way to provide an indication of different uplinic resources for potentially many different terminal devices-I-Iowevcr, it will be appreciated other schemes for indicating which uplink resource to use may be provided. For example, if there are one hundred terminal devices (e.g. vending machines) within a base station's cell footprint subscribing to a given multicast service, an eNocleB may simply allocate them with one hundred consecutive C-R.NTIs. Each terminal device may then derive an appropriate upl.inlc resource to use for ACK / NACIK siguafling based on its C-RNTI For example. with a carrier t]iat can accommodate n ACK / NACK responses l'' sub-frame, a terminal device with C-RJ'i['l "7 might be configured to respond to a multicast transmission S in sub-frame i in a sub-frame i + 4 + FLOOR(Z/n,), using a resource will-un the sub-frame based on the fraction part of 7/n.

It wil.1 be appreciated that variot.is modifications can be made to the embodiments described above without departing from the scope of the present invention as defined in the appended claims.

For example, while the above description has fOcussed on an implementation of the invention in a virtual carrier context, it will he appreciated that other example embodiments of the invention may he implemented in otherwise conventional telecommunication systems, for example, which might not support a virIl2al carrier of the kind, described above.

Furthermore, although embodiments of the invention have been described with refei-ence to an LIE mobile radio network, it will be appreciated that the present invention can be applied to other forms of network such as USM, 3G / IJMTS, CDMA2000, etc. The term MTC tenninal as used herein can be replaced with user equipment (UE), mobile communications device, terminal device etc. Furthermore, althougji the term base station has been used interchangeably with eNodeB it should be understood that there is no difference in ftnctionalily between these network entities.

Thus, there has been described a method of communicating data between a base station and a plurality of tenmnal devices in a wireless telecommunications system is described., The method comprises transmitting data from the base station to the plurality of temuinal devices in a multicast transmission and transmitting response signals from the terminal devices to the base station to indicate whether or not the respective terminal devices have successflully received the multicast transmission. The use of a multicast transmission provides an efficient mechanism for communicating the same data to a plurality of terminal device, for example a.s might be desired in a machine-type communicati.on network. In combination with this, the use of individual response signais, such as ACK. I NACIK.

signalling, from the terminal devices allows the base station, or other entity, such as a machine-type communications server, to track which terminal devices have indicated successfUl receipt of the multicast transmission, and to instigate an appropriate re-lransmi.5sion protocol accordi ngly further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. It* *will be appreciated that features of the S dependent claims may be combined with features of the independent claims in combinations other than those explicitly set out in the claim&

REFERENCES

[1] FISI Is 122 368 V1O.530 (2011-07)/ 3(1W? IS 22368 version 105.0 Release 10) [2] UK patent application GB 1101970 0 [.3] UK patent pp1ieation GB 1101981 7 4] UK patent application GB 11019668 [5] UK patent application GB 1101983 3 [6] UK.patent application GB 11018538 [7] UK patent application GB 1101982.5 [8] UK patent application GB 11019809 [9] UK patent application GB 1101972.6 [10] ETSE IS 136 213 V10.2,0 (201 1-06)/ 3GPP TS 36.213 version 10.2.0 Release 10) [11] ETS1 IS 136321 V10..2.0 (2011-06) / 3GPP TS 36.321 version 102.0 Release 10)

Claims (1)

1. <claim-text>CLAIMS1. A method of communicating data in a wireless telecommunications system, the method comprising: transmitting data from a base station to a plurality of terminal devices in. a multicast transmission; and tTansmittrng response signals from respective ones of the terminal devices to the base station in response to the multicast transmission to indicate whether the respective terminal devices have successfully received the multicast transmission. l0</claim-text> <claim-text>2 The method of claim 1, further comprising conveying to respective ones of the terminal devices an indication of an uplink transmission resoince to be used for their response signal.</claim-text> <claim-text>3. The method of claim 2, wherein the indication of an uplink transmission resource is conveyed during a set-up procedure performed when the respective teiminal devices connect to the wireless telecommunications system..</claim-text> <claim-text>4, The method of claim 2, wherein the set-up procedure comprises a Radio Resource Connection request..</claim-text> <claim-text>5.. The method of claim 2, wherein the indication of an uplink transmission resource is conveyed in association with the multicast transmission..</claim-text> <claim-text>6-The method of any of claims 2 to 5, wherein the indication of an uplink transmission resource is conveyed by explicit signalling.</claim-text> <claim-text>7.. The method of any of claims 2 to 5, wherein the indication of an uplink transmission resource is conveyed by implicit signalling.</claim-text> <claim-text>8. The method of claim 7, wherein the indication of an uplirik transmission resource is conveyed within a radio network identifier, 9. The method of any of claims 2 to 8, whcrein the indication of an upink txansmission jesouree comprises at least one of an indication of a transmission resource within an uplink sub-frame, an indication of an uplinic sub-frame, and an indication of an uplink canier 10. The method of any of claims 1 to 9, wherein the i-espouse signals are transmitted on a Physical Uplink Control Channel, PUCCH 11 The method of any of claims 1 to 10, wherein the]-esponse signals are transmitted in an upli.nk sub-frame of the wireless telecommunications system occurring at a time derived from the time of a downl.inlc sub-frame containing the rnulticast transmission.12. The method of any of claims 1 to 11, wherein diffcrent ones of the terminal devices transmit their response signals in different upl.ink sub-frames and / or carriers of the wireless telecommunications system..13. The method of any of claims 1 to 12, fimrthcr comprising detennining from the response signals received at the base station whether any terminal device has not received the multicast transmission, and if so, re-transmitting the data from the base station.14. The method of any of claims 1 to 13, wherei.n response signals from diffement oncs of the terminal devices are transmitted using different* *upIc transmission resources.15. The method of an.y of claims I to 1.4, wherein the wireless telecommunications system operates in downlink over a first frequency bandwidth and in uplink over a second frequency bandwidth, and wherein the multicast transmission is made using downlink trans-mission resources on frequencies selected from within a third frequency bandwidth which is smaller than and within the first frequency bandwidth; and wherein the response signals from the terminal devices are transmitted using uplink transmission resources on frequencies selected from within a fourth frequency bandwidth which is smaller than and within the second frequency bandwidth.1 6.. The method of claim 15, wherein the first and second frequency bandwidths are the same width and / or the third and fourth frequency bandwidths are the same width.17. A wireless telecommunications system comprising a base station and a plurality of termir.al devices, wherein the base station is configured to transmit data to a plurality of terminal devices in a multicast transmission, and wherein the terminal devices are configured to tnmsmit response signals to the base station in response to the multicast transmission to indicate whether they have successthlly received the multicast transmission..IS. The wireless telecommunications system of claim 17, wherein the base station is further configured to convey to respective ones of the terminal devices an indication of an uplink ttansmission resource to he used for their response sigual.19., The wireless telecommunications system of claim 18, wherein the base station is configured to convey the indication of an uplink transmission resource during a set-up procedure performed when the respective terminal devices corwect to the wireless teleconununications systcm..20,. The wireless telecommunications system of claim 18, wherein the set-up procedure compriscs a Radio Resource Connection request.21., The wireless telecommunications system of claim 18, wherein the base station is configured to convey the indication of an uplink transmission resource in association with the multi cast Iransniiss iorn 22.. The wireless telecommunications system of any of claims 18 to 21, wherein the base station is configured to convey the indication of an uplink transmission resource by explicit signalling.73 The wireless telecommunicalions system of any of claims 18 to 21, wherein the base station is configured to convey the indication of an uplink transmission resource by implicit signalling.24.. The wireless telecommunications system of claim 23, wherein the base station is configured to convey the indication of an uplink transmission resource within a radio network identifier allocated to the respective terminal devices 25. The wireless telecommunications system of any of claims 1 8 to 24, wherein the indication of an uplinlc transmission resource comprises at least one of an indication of a nausmission resource within an uplink sub-frame, an indication of an uplink sub-frame, and an indication of an uplink carrier 26. The wireless telecommunications system of any of claims 17 to 25, wherein 1 5 the terminal devices are configured to transmit the response signals on a Physical Uplinic Control Channel, PUCCH.27 The wireless telecommunications system of any of claims 17 to 26, wherein the terminal devices are configured to transmit the response signals in an uplin.lc sub-frame of the wireless telecommunications system occurring at a time derived from the time of a downlink sub-frame containing the multicast transmission 28. The wireless telecommunications system of any of claims 17 to 27, wherein different ones of the terminal devices are arranged to transmit their response signals in different uplink sub-frames and / or earners of the wireless telecommunications system.29-The wireless telecommunications system of any of claims 17 to 28, wherein th.e base station is configured to determine from the response signals whether any terminal device has not received a multicast transmission, and if so, to re-transmit the data.30. The. wireless telecommunications system of any of claims 7 to 2B, wherein different ones of the terminal devices are arranged to transmit their response signals using different uplink transmission resources..31.. The wireless telecojunjunications system of any of claims 17 to.30, wherein the wireless telecommunications system operates in downlink over a first frequency bandwidth and in uplink over a second frequency bandwidth, and the base station is configured to transmit the multicast transmission using downlink transmission resources on frequencies selected from within a third frequency bandwidth which is smaller than and within the first frequency bandwidth; and wherein the terminal devices are configured to transmit their response siguals using uplink transmission resources on frequencies selected from within a fourth frequency bandwidth which is smaller than and within the second frequency bandwidth..32. The wireless Eelecornnmnications system of claim 31, wherein the first and second frequency bandwidths are the same width arid / or the third and fourth frequency bandwidths are the same width.3.3. A method of operating a terminal device fOr the communication data in a wireless telecommunications system, the method comprising: receiving data transmitted by a base station to a plurality of terminal devices in a multicast transmission; and bansnñtting a response signal to the base station in response to the multicast transmission to indicate whether the terminal device successfully received the multicast transmission.34.. The metlwd of, claim 33, farther' comprising obtaining an indication of an uplink transmission resource to be used by the terminal device for the response signal..35. The method of claim 34, wherein the indication of an uplink transmission resource is obtained from information conveyed to the terminal device during a set-up procedure performed when the terminal devices initiates a connection to the base station.36 The method of claim 34, wherein the set-up procedure comprises a Radio Resource Connection request 37.. The method of claim 34, wherein the indication of an ujlink transmission resource is obtained from infbrmation conveyed to the terminal device in association with the multicast trarisrnissi on.38. The method of any of claim.s 34 to 37, wherein the indication of an uplink transrni3sion resource is obtained from information conveyed to the terminal device by explicit signalling.39. The method of any of claims 34 to 37, wherein the indication of an uplink transmission resource is obtained from in.fonnation conveyed to the terminal device by 1 5 implicit signalling.The method of claim 39, whercin the indication of an upli.nlc transmission resource is obtained from a radi.o networlc identifier allocated by the base station.41. The method of any of claims 34 to 40, wherein the indication of an uplink transmission resource comprises at least one of an indication of a transmission resource within an uplink sub-flame, an indication of an uplink sub-frame, and an indication of an uplink carrier.42. The method of any of claims 33 to 41, wherein the response signal is transmitted on a Physical Uplink Control Channel, PUCCH.43. The method of any of claims 33 to 42, wherein the response signal is transmitted in an uplinic sub-frame of the wireless telecommunications system occurring at a time derived fiom the time of a downlinlc sub-flame containing the multicast transmission.44.. The method of any of claims 33 to 43, wherein the response signal is transmitted in a different uplink sub-frames and I or cairier of the wireless teleconununications system as compared to a corresponding response signal from another terminal device..45. The method of any of claims 33 to 4.3, ftrther comprising receiving a re-transmission of the data. in the event the terminal device transmits a response signal indicating the multicast transmission was not successfully received.46.. The method of any of claims 33 to 45, wherein the response signal is transmitted using uplinic transmission resources which are specific to the terminal device..47. The method of any of' claims.33 to 46, wherein the wireless telecommunications system operates in downlink over a first frequency bandwidth and in uplinlc over a second frequency bandwidth, and wherein the multicast transmission is received using downli.nlc transmission resources on frequencies selected from within a third frequency bandwidth which is smaller than arid within the first frequency bandwidth; and wherein the response sigual is transmitted. using uplinic transmission resources on frequencies selected from within a fourth frequency bandwidth which is smaller than and within the second frequency bandwidth..48. The method of' claim 47, wherein the first and second frequency bandwidths are the same width and I or the third and fourth frequency bandwidths are the same width.49.. A terminal device for receiving data in a wireless telecommunications system, wherein the terminal device is configured to receive data. transmitted by a base station to a plurality of' terminal devices in a multicast transmission, and wherein the terminal device is further configured to transmit a response signal to the base station in response to the multicast transmission to indicate whether the terminal device successfully received the multicast transmission.50. The terminal device of claim 49, wherein the tenninal device is configured to obtain an indication of an uplink. transmission resource to he used for the response signal 51 The terminal device of claim 50, wherein the ten-nina] device is configured to obtain the indication of an uplink transmission resource from infonnation conveyed during a set-up procedure performed when the tcrninaI device connects to the wire'ess teleconimuni cations system.52.. The teirninal device of claim 50, wherein the set-up procedure comprises a 1 0 Radio Resource Connection request.53.. The terminal devicc of claim 50, wherein the terminal device is configured to obtain the indication of an uplink transmission resource from information conveyed in.association with the multica.st transmission.54.. The terminal device of any of claims 30 to 53, wherein the terminal device is configured obtain the indication of an uplink transmission resource from information conveyed by explicit signalling..55. The terminal device of any of claims 50 to 53, wherein the terminal device is configured obtain the indication of an uplink transmission resource from information conveyed by implicit signalling.56. The terminal device of claim 55, wherein the terminal device is configured to obtain the indication of an uplink transmission resource fiom information conveyed within a radio network identifier allocated to the respective terminal devices.57. The terminal device of any of claims 50 to 56, wherein the indication of an uplink transmission resource comprises at least one of an indication of a transmission resource within an uplink sub-frame, an indication of an upliak sub-frame, and an indication of an uplink carrier.SE. The terminal device of any of claims 49 to 57, wherein tile temñnal device is configured to transmit the response signal on a Physical Uphnk Control Channel, PUCCH..59. The terminal device of any of claims 47 to 58, wherein the terminal device is configured to transmit the response signal in an uplinic sub-frame of the wireless telecommunications system occurring at a time derived from the time of a downlink sub-frame containing the multicast transmission.60., The terminal device of any of claims 49 to 59. wherein the terminal device is configured to transmit the response signal in a different uplink sub-frames and / or carrier of the wireless telecommunications system as compared to a corresponding response signal from another terminal device.61, The terminal device of any of claims 49 to 60, wherein the terminal device is 1 5 operable to receive a re-transmission of the data in the event the terrnina.I device transmits a response signal indicating the multicast transmission was not successflu]ly received.62.. The terminal device of' any of claims 49 to 61, wherein the terminal. device is configured to transmit the response signal using uplinic transmission resources which ai-e specific to the temilnal device for the inulticast transmission, 63.. The terminal device of any of claims 49 to 62. wherein the wireless teleconimunications system operates in downlink over a first frequency bandwidth and in uplinic over a second frequency bandwidth, and the terminal device is configured to receive the multicast transmission using downlink transmission resources on frequencies selected from within a. third frequency bandwidth which is smaller than and within the first frequency bandwidth; and to transmit tile response signal using uplink. transmission resources on frequcneies selected from within a fourth frequency bandwidth which is smaller than and within the second frequency bandwidth.64. The terminal device of claim 63, wherein the first and second frequency bandwidths are the same width and / or the third and fourth frequency bandwidl.hs are the same width..65. A method substantially as hereinbefore described with reference to Figures 5 to 22 of the accompanying drawings.66.. A wireless telecommunications system or terminal device substantially as hereinbefore described with reference to Figures 5 to 22 of the accompanying drawings.</claim-text>